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 $163.56   11.738%   $182.7587   $182.76   $182.75   $182.80  
  Purchase #2 $9.92   8.266%   $10.74   $10.74   $10.75   $10.70  
  Purchase #3 $13.83   9.499%   $15.1437   $15.14   $15.15   $15.10  
  Purchase #4 $240.26   3.825%   $249.4499   $249.45   $249.45   $249.40  
  Purchase #5 $44.34   9.289%   $48.4587   $48.46   $48.45   $48.50  
  Purchase #6 $170.84   4.770%   $178.9891   $178.99   $179.00   $179.00  
  Purchase #7 $57.47   5.862%   $60.8389   $60.84   $60.85   $60.80  
  7 purchase totals = $700.22       $746.3790   $746.38   $746.40   $746.30