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 $114.53   9.627%   $125.5558   $125.56   $125.55   $125.60  
  Purchase #2 $73.56   10.433%   $81.2345   $81.23   $81.25   $81.20  
  Purchase #3 $59.90   9.631%   $65.669   $65.67   $65.65   $65.70  
  Purchase #4 $202.63   11.674%   $226.285   $226.29   $226.30   $226.30  
  Purchase #5 $110.86   8.532%   $120.3186   $120.32   $120.30   $120.30  
  Purchase #6 $72.95   3.804%   $75.725   $75.73   $75.75   $75.70  
  Purchase #7 $100.77   6.704%   $107.5256   $107.53   $107.55   $107.50  
  7 purchase totals = $735.20       $802.3135   $802.33   $802.35   $802.30