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 $50.38   11.613%   $56.2306   $56.23   $56.25   $56.20  
  Purchase #2 $206.95   13.523%   $234.9358   $234.94   $234.95   $234.90  
  Purchase #3 $225.77   10.520%   $249.521   $249.52   $249.50   $249.50  
  Purchase #4 $50.43   10.140%   $55.5436   $55.54   $55.55   $55.50  
  Purchase #5 $44.96   5.580%   $47.4688   $47.47   $47.45   $47.50  
  Purchase #6 $235.87   8.566%   $256.0746   $256.07   $256.05   $256.10  
  Purchase #7 $129.25   13.409%   $146.5811   $146.58   $146.60   $146.60  
  7 purchase totals = $943.61       $1,046.3555   $1,046.35   $1,046.35   $1,046.30