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 $126.95   6.171%   $134.7841   $134.78   $134.80   $134.80  
  Purchase #2 $95.37   6.432%   $101.5042   $101.50   $101.50   $101.50  
  Purchase #3 $49.48   4.429%   $51.6715   $51.67   $51.65   $51.70  
  Purchase #4 $80.56   3.341%   $83.2515   $83.25   $83.25   $83.30  
  Purchase #5 $116.25   8.309%   $125.9092   $125.91   $125.90   $125.90  
  Purchase #6 $237.77   4.848%   $249.2971   $249.30   $249.30   $249.30  
  Purchase #7 $13.44   9.803%   $14.7575   $14.76   $14.75   $14.80  
  7 purchase totals = $719.82       $761.1751   $761.17   $761.15   $761.30