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 $245.25   12.544%   $276.0142   $276.01   $276.00   $276.00  
  Purchase #2 $139.50   5.183%   $146.7303   $146.73   $146.75   $146.70  
  Purchase #3 $227.45   9.597%   $249.2784   $249.28   $249.30   $249.30  
  Purchase #4 $244.72   13.777%   $278.4351   $278.44   $278.45   $278.40  
  Purchase #5 $245.44   10.408%   $270.9854   $270.99   $271.00   $271.00  
  Purchase #6 $164.68   10.538%   $182.034   $182.03   $182.05   $182.00  
  Purchase #7 $75.44   4.241%   $78.6394   $78.64   $78.65   $78.60  
  7 purchase totals = $1,342.48       $1,482.1168   $1,482.12   $1,482.20   $1,482.00