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 $204.79   4.816%   $214.6527   $214.65   $214.65   $214.70  
  Purchase #2 $70.48   8.346%   $76.3623   $76.36   $76.35   $76.40  
  Purchase #3 $210.95   11.729%   $235.6923   $235.69   $235.70   $235.70  
  Purchase #4 $225.97   10.355%   $249.3692   $249.37   $249.35   $249.40  
  Purchase #5 $164.40   12.641%   $185.1818   $185.18   $185.20   $185.20  
  Purchase #6 $111.71   12.593%   $125.7776   $125.78   $125.80   $125.80  
  Purchase #7 $158.45   6.404%   $168.5971   $168.60   $168.60   $168.60  
  7 purchase totals = $1,146.75       $1,255.6330   $1,255.63   $1,255.65   $1,255.80