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 $68.33   7.168%   $73.2279   $73.23   $73.25   $73.20  
  Purchase #2 $52.41   4.470%   $54.7527   $54.75   $54.75   $54.80  
  Purchase #3 $133.94   11.209%   $148.9533   $148.95   $148.95   $149.00  
  Purchase #4 $58.72   9.732%   $64.4346   $64.43   $64.45   $64.40  
  Purchase #5 $51.62   5.680%   $54.552   $54.55   $54.55   $54.60  
  Purchase #6 $209.49   12.113%   $234.8655   $234.87   $234.85   $234.90  
  Purchase #7 $182.42   13.271%   $206.629   $206.63   $206.65   $206.60  
  7 purchase totals = $756.93       $837.4150   $837.41   $837.45   $837.50