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 $241.67   10.302%   $266.5668   $266.57   $266.55   $266.60  
  Purchase #2 $151.58   7.324%   $162.6817   $162.68   $162.70   $162.70  
  Purchase #3 $121.43   3.521%   $125.7056   $125.71   $125.70   $125.70  
  Purchase #4 $210.73   7.568%   $226.678   $226.68   $226.70   $226.70  
  Purchase #5 $245.82   11.720%   $274.6301   $274.63   $274.65   $274.60  
  Purchase #6 $207.61   10.106%   $228.5911   $228.59   $228.60   $228.60  
  Purchase #7 $157.47   13.192%   $178.2434   $178.24   $178.25   $178.20  
  7 purchase totals = $1,336.31       $1,463.0967   $1,463.10   $1,463.15   $1,463.10