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 $43.51   12.503%   $48.9501   $48.95   $48.95   $49.00  
  Purchase #2 $250.70   8.399%   $271.7563   $271.76   $271.75   $271.80  
  Purchase #3 $89.90   4.849%   $94.2593   $94.26   $94.25   $94.30  
  Purchase #4 $142.92   9.597%   $156.636   $156.64   $156.65   $156.60  
  Purchase #5 $141.31   5.641%   $149.2813   $149.28   $149.30   $149.30  
  Purchase #6 $14.33   8.501%   $15.5482   $15.55   $15.55   $15.50  
  Purchase #7 $91.68   6.553%   $97.6878   $97.69   $97.70   $97.70  
  7 purchase totals = $774.35       $834.1190   $834.13   $834.15   $834.20