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 $180.53   10.508%   $199.5001   $199.50   $199.50   $199.50  
  Purchase #2 $183.76   5.716%   $194.2637   $194.26   $194.25   $194.30  
  Purchase #3 $66.28   3.834%   $68.8212   $68.82   $68.80   $68.80  
  Purchase #4 $187.96   9.369%   $205.57   $205.57   $205.55   $205.60  
  Purchase #5 $87.29   12.332%   $98.0546   $98.05   $98.05   $98.10  
  Purchase #6 $59.59   5.605%   $62.93   $62.93   $62.95   $62.90  
  Purchase #7 $102.59   4.629%   $107.3389   $107.34   $107.35   $107.30  
  7 purchase totals = $868.00       $936.4785   $936.47   $936.45   $936.50