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 $54.84   13.259%   $62.1112   $62.11   $62.10   $62.10  
  Purchase #2 $42.69   12.241%   $47.9157   $47.92   $47.90   $47.90  
  Purchase #3 $130.77   12.368%   $146.9436   $146.94   $146.95   $146.90  
  Purchase #4 $164.85   11.584%   $183.9462   $183.95   $183.95   $183.90  
  Purchase #5 $158.98   13.549%   $180.5202   $180.52   $180.50   $180.50  
  Purchase #6 $208.53   6.135%   $221.3233   $221.32   $221.30   $221.30  
  Purchase #7 $182.95   7.772%   $197.1689   $197.17   $197.15   $197.20  
  7 purchase totals = $943.61       $1,039.9291   $1,039.93   $1,039.85   $1,039.80