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 $215.34   8.721%   $234.1198   $234.12   $234.10   $234.10  
  Purchase #2 $30.53   12.226%   $34.2626   $34.26   $34.25   $34.30  
  Purchase #3 $58.56   6.379%   $62.2955   $62.30   $62.30   $62.30  
  Purchase #4 $118.35   11.858%   $132.3839   $132.38   $132.40   $132.40  
  Purchase #5 $188.66   13.844%   $214.7781   $214.78   $214.80   $214.80  
  Purchase #6 $216.29   12.178%   $242.6298   $242.63   $242.65   $242.60  
  Purchase #7 $30.89   13.229%   $34.9764   $34.98   $35.00   $35.00  
  7 purchase totals = $858.62       $955.4461   $955.45   $955.50   $955.50