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 $185.56   10.586%   $205.2034   $205.20   $205.20   $205.20  
  Purchase #2 $34.80   8.314%   $37.6933   $37.69   $37.70   $37.70  
  Purchase #3 $94.63   10.644%   $104.7024   $104.70   $104.70   $104.70  
  Purchase #4 $188.71   3.697%   $195.6866   $195.69   $195.70   $195.70  
  Purchase #5 $84.41   9.730%   $92.6231   $92.62   $92.60   $92.60  
  Purchase #6 $125.52   4.358%   $130.9902   $130.99   $131.00   $131.00  
  Purchase #7 $250.60   9.699%   $274.9057   $274.91   $274.90   $274.90  
  7 purchase totals = $964.23       $1,041.8047   $1,041.80   $1,041.80   $1,041.80