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 $42.45   10.697%   $46.9909   $46.99   $47.00   $47.00  
  Purchase #2 $178.94   12.311%   $200.9693   $200.97   $200.95   $201.00  
  Purchase #3 $28.72   5.778%   $30.3794   $30.38   $30.40   $30.40  
  Purchase #4 $208.77   12.248%   $234.3401   $234.34   $234.35   $234.30  
  Purchase #5 $144.75   11.448%   $161.321   $161.32   $161.30   $161.30  
  Purchase #6 $203.57   10.500%   $224.9449   $224.94   $224.95   $224.90  
  Purchase #7 $61.41   6.642%   $65.4889   $65.49   $65.50   $65.50  
  7 purchase totals = $868.61       $964.4345   $964.43   $964.45   $964.40