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 $31.53   12.397%   $35.4388   $35.44   $35.45   $35.40  
  Purchase #2 $108.70   10.309%   $119.9059   $119.91   $119.90   $119.90  
  Purchase #3 $103.54   4.284%   $107.9757   $107.98   $108.00   $108.00  
  Purchase #4 $218.76   6.582%   $233.1588   $233.16   $233.15   $233.20  
  Purchase #5 $188.86   11.764%   $211.0775   $211.08   $211.10   $211.10  
  Purchase #6 $45.63   5.125%   $47.9685   $47.97   $47.95   $48.00  
  Purchase #7 $194.65   13.733%   $221.3813   $221.38   $221.40   $221.40  
  7 purchase totals = $891.67       $976.9065   $976.92   $976.95   $977.00