Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.38   10.349%   $240.9801   $240.98   $241.00   $241.00  
  Purchase #2 $112.64   12.409%   $126.6175   $126.62   $126.60   $126.60  
  Purchase #3 $116.41   11.856%   $130.2116   $130.21   $130.20   $130.20  
  Purchase #4 $215.76   8.616%   $234.3499   $234.35   $234.35   $234.30  
  Purchase #5 $218.87   5.757%   $231.4703   $231.47   $231.45   $231.50  
  Purchase #6 $220.57   10.762%   $244.3077   $244.31   $244.30   $244.30  
  Purchase #7 $126.60   13.803%   $144.0746   $144.07   $144.05   $144.10  
  7 purchase totals = $1,229.23       $1,352.0117   $1,352.01   $1,351.95   $1,352.00