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 $176.27   3.797%   $182.963   $182.96   $182.95   $183.00  
  Purchase #2 $115.38   3.750%   $119.7068   $119.71   $119.70   $119.70  
  Purchase #3 $73.42   8.634%   $79.7591   $79.76   $79.75   $79.80  
  Purchase #4 $130.31   13.612%   $148.0478   $148.05   $148.05   $148.00  
  Purchase #5 $200.58   6.810%   $214.2395   $214.24   $214.25   $214.20  
  Purchase #6 $229.43   10.835%   $254.2887   $254.29   $254.30   $254.30  
  Purchase #7 $58.94   9.849%   $64.745   $64.75   $64.75   $64.70  
  7 purchase totals = $984.33       $1,063.7499   $1,063.76   $1,063.75   $1,063.70