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 $51.36   3.543%   $53.1797   $53.18   $53.20   $53.20  
  Purchase #2 $214.26   4.733%   $224.4009   $224.40   $224.40   $224.40  
  Purchase #3 $47.96   10.647%   $53.0663   $53.07   $53.05   $53.10  
  Purchase #4 $198.91   12.354%   $223.4833   $223.48   $223.50   $223.50  
  Purchase #5 $59.96   11.707%   $66.9795   $66.98   $67.00   $67.00  
  Purchase #6 $168.41   8.438%   $182.6204   $182.62   $182.60   $182.60  
  Purchase #7 $173.29   3.130%   $178.714   $178.71   $178.70   $178.70  
  7 purchase totals = $914.15       $982.4441   $982.44   $982.45   $982.50