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 $60.45   4.646%   $63.2585   $63.26   $63.25   $63.30  
  Purchase #2 $56.68   3.871%   $58.8741   $58.87   $58.85   $58.90  
  Purchase #3 $206.71   4.277%   $215.551   $215.55   $215.55   $215.60  
  Purchase #4 $57.34   11.632%   $64.0098   $64.01   $64.00   $64.00  
  Purchase #5 $211.98   11.781%   $236.9534   $236.95   $236.95   $237.00  
  Purchase #6 $231.31   4.736%   $242.2648   $242.26   $242.25   $242.30  
  Purchase #7 $50.53   8.615%   $54.8832   $54.88   $54.90   $54.90  
  7 purchase totals = $875.00       $935.7948   $935.78   $935.75   $936.00