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 $91.88   5.728%   $97.1429   $97.14   $97.15   $97.10  
  Purchase #2 $228.59   10.841%   $253.3714   $253.37   $253.35   $253.40  
  Purchase #3 $54.25   6.104%   $57.5614   $57.56   $57.55   $57.60  
  Purchase #4 $68.83   10.361%   $75.9615   $75.96   $75.95   $76.00  
  Purchase #5 $152.58   4.482%   $159.4186   $159.42   $159.40   $159.40  
  Purchase #6 $214.47   4.445%   $224.0032   $224.00   $224.00   $224.00  
  Purchase #7 $46.68   8.326%   $50.5666   $50.57   $50.55   $50.60  
  7 purchase totals = $857.28       $918.0256   $918.02   $917.95   $918.10