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 $249.26   6.465%   $265.3747   $265.37   $265.35   $265.40  
  Purchase #2 $17.44   4.554%   $18.2342   $18.23   $18.25   $18.20  
  Purchase #3 $146.79   13.205%   $166.1736   $166.17   $166.15   $166.20  
  Purchase #4 $45.62   12.865%   $51.489   $51.49   $51.50   $51.50  
  Purchase #5 $109.81   8.281%   $118.9034   $118.90   $118.90   $118.90  
  Purchase #6 $101.89   4.259%   $106.2295   $106.23   $106.25   $106.20  
  Purchase #7 $199.36   9.290%   $217.8805   $217.88   $217.90   $217.90  
  7 purchase totals = $870.17       $944.2849   $944.27   $944.30   $944.30