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 $235.95   12.146%   $264.6085   $264.61   $264.60   $264.60  
  Purchase #2 $155.77   10.215%   $171.6819   $171.68   $171.70   $171.70  
  Purchase #3 $182.78   8.190%   $197.7497   $197.75   $197.75   $197.70  
  Purchase #4 $18.45   8.746%   $20.0636   $20.06   $20.05   $20.10  
  Purchase #5 $62.73   5.818%   $66.3796   $66.38   $66.40   $66.40  
  Purchase #6 $129.37   3.153%   $133.449   $133.45   $133.45   $133.40  
  Purchase #7 $140.35   11.474%   $156.4538   $156.45   $156.45   $156.50  
  7 purchase totals = $925.40       $1,010.3861   $1,010.38   $1,010.40   $1,010.40