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 $214.42   8.170%   $231.9381   $231.94   $231.95   $231.90  
  Purchase #2 $126.37   10.581%   $139.7412   $139.74   $139.75   $139.70  
  Purchase #3 $214.81   9.821%   $235.9065   $235.91   $235.90   $235.90  
  Purchase #4 $135.59   8.250%   $146.7762   $146.78   $146.80   $146.80  
  Purchase #5 $250.82   9.569%   $274.821   $274.82   $274.80   $274.80  
  Purchase #6 $217.42   11.161%   $241.6862   $241.69   $241.70   $241.70  
  Purchase #7 $50.56   5.442%   $53.3115   $53.31   $53.30   $53.30  
  7 purchase totals = $1,209.99       $1,324.1807   $1,324.19   $1,324.20   $1,324.10