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 $125.53   8.217%   $135.8448   $135.84   $135.85   $135.80  
  Purchase #2 $239.62   13.644%   $272.3138   $272.31   $272.30   $272.30  
  Purchase #3 $118.58   13.314%   $134.3677   $134.37   $134.35   $134.40  
  Purchase #4 $249.49   4.480%   $260.6672   $260.67   $260.65   $260.70  
  Purchase #5 $119.81   4.425%   $125.1116   $125.11   $125.10   $125.10  
  Purchase #6 $214.61   12.748%   $241.9685   $241.97   $241.95   $242.00  
  Purchase #7 $66.61   13.314%   $75.4785   $75.48   $75.50   $75.50  
  7 purchase totals = $1,134.25       $1,245.7521   $1,245.75   $1,245.70   $1,245.80