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 $57.43   6.823%   $61.3484   $61.35   $61.35   $61.30  
  Purchase #2 $221.68   11.265%   $246.6523   $246.65   $246.65   $246.70  
  Purchase #3 $129.50   10.733%   $143.3992   $143.40   $143.40   $143.40  
  Purchase #4 $104.89   12.443%   $117.9415   $117.94   $117.95   $117.90  
  Purchase #5 $218.92   8.612%   $237.7734   $237.77   $237.75   $237.80  
  Purchase #6 $72.58   9.648%   $79.5825   $79.58   $79.60   $79.60  
  Purchase #7 $93.98   4.664%   $98.3632   $98.36   $98.35   $98.40  
  7 purchase totals = $898.98       $985.0605   $985.05   $985.05   $985.10