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 $201.31   12.544%   $226.5623   $226.56   $226.55   $226.60  
  Purchase #2 $31.53   5.105%   $33.1396   $33.14   $33.15   $33.10  
  Purchase #3 $68.38   8.397%   $74.1219   $74.12   $74.10   $74.10  
  Purchase #4 $7.49   11.597%   $8.3586   $8.36   $8.35   $8.40  
  Purchase #5 $208.78   6.692%   $222.7516   $222.75   $222.75   $222.80  
  Purchase #6 $56.36   3.343%   $58.2441   $58.24   $58.25   $58.20  
  Purchase #7 $118.79   9.728%   $130.3459   $130.35   $130.35   $130.30  
  7 purchase totals = $692.64       $753.5240   $753.52   $753.50   $753.50