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 $82.85   11.873%   $92.6868   $92.69   $92.70   $92.70  
  Purchase #2 $164.62   12.749%   $185.6074   $185.61   $185.60   $185.60  
  Purchase #3 $125.64   3.659%   $130.2372   $130.24   $130.25   $130.20  
  Purchase #4 $64.80   7.837%   $69.8784   $69.88   $69.90   $69.90  
  Purchase #5 $104.93   10.814%   $116.2771   $116.28   $116.30   $116.30  
  Purchase #6 $111.91   12.778%   $126.2099   $126.21   $126.20   $126.20  
  Purchase #7 $233.90   7.129%   $250.5747   $250.57   $250.55   $250.60  
  7 purchase totals = $888.65       $971.4715   $971.48   $971.50   $971.50