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 $114.56   6.708%   $122.2447   $122.24   $122.25   $122.20  
  Purchase #2 $151.39   13.151%   $171.2993   $171.30   $171.30   $171.30  
  Purchase #3 $210.29   13.229%   $238.1093   $238.11   $238.10   $238.10  
  Purchase #4 $68.84   7.398%   $73.9328   $73.93   $73.95   $73.90  
  Purchase #5 $68.53   10.770%   $75.9107   $75.91   $75.90   $75.90  
  Purchase #6 $167.26   6.159%   $177.5615   $177.56   $177.55   $177.60  
  Purchase #7 $101.92   3.157%   $105.1376   $105.14   $105.15   $105.10  
  7 purchase totals = $882.79       $964.1959   $964.19   $964.20   $964.10