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 $59.53   7.799%   $64.1727   $64.17   $64.15   $64.20  
  Purchase #2 $194.62   8.166%   $210.5127   $210.51   $210.50   $210.50  
  Purchase #3 $241.49   6.172%   $256.3948   $256.39   $256.40   $256.40  
  Purchase #4 $33.51   6.835%   $35.8004   $35.80   $35.80   $35.80  
  Purchase #5 $158.94   7.325%   $170.5824   $170.58   $170.60   $170.60  
  Purchase #6 $103.80   6.853%   $110.9134   $110.91   $110.90   $110.90  
  Purchase #7 $75.72   12.115%   $84.8935   $84.89   $84.90   $84.90  
  7 purchase totals = $867.61       $933.2699   $933.25   $933.25   $933.30