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 $231.71   12.750%   $261.253   $261.25   $261.25   $261.30  
  Purchase #2 $14.34   5.804%   $15.1723   $15.17   $15.15   $15.20  
  Purchase #3 $92.54   11.262%   $102.9619   $102.96   $102.95   $103.00  
  Purchase #4 $91.39   5.709%   $96.6075   $96.61   $96.60   $96.60  
  Purchase #5 $119.91   7.533%   $128.9428   $128.94   $128.95   $128.90  
  Purchase #6 $217.67   7.799%   $234.6461   $234.65   $234.65   $234.60  
  Purchase #7 $69.46   7.512%   $74.6778   $74.68   $74.70   $74.70  
  7 purchase totals = $837.02       $914.2614   $914.26   $914.25   $914.30