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 $66.55   4.104%   $69.2812   $69.28   $69.30   $69.30  
  Purchase #2 $55.40   5.802%   $58.6143   $58.61   $58.60   $58.60  
  Purchase #3 $238.76   7.420%   $256.476   $256.48   $256.50   $256.50  
  Purchase #4 $107.63   7.197%   $115.3761   $115.38   $115.40   $115.40  
  Purchase #5 $97.47   8.266%   $105.5269   $105.53   $105.55   $105.50  
  Purchase #6 $213.86   12.649%   $240.9112   $240.91   $240.90   $240.90  
  Purchase #7 $112.49   6.845%   $120.1899   $120.19   $120.20   $120.20  
  7 purchase totals = $892.16       $966.3756   $966.38   $966.45   $966.40