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 $132.99   13.767%   $151.2987   $151.30   $151.30   $151.30  
  Purchase #2 $191.88   12.378%   $215.6309   $215.63   $215.65   $215.60  
  Purchase #3 $98.70   12.230%   $110.771   $110.77   $110.75   $110.80  
  Purchase #4 $101.46   10.856%   $112.4745   $112.47   $112.45   $112.50  
  Purchase #5 $157.33   10.327%   $173.5775   $173.58   $173.60   $173.60  
  Purchase #6 $227.85   3.859%   $236.6427   $236.64   $236.65   $236.60  
  Purchase #7 $202.33   4.201%   $210.8299   $210.83   $210.85   $210.80  
  7 purchase totals = $1,112.54       $1,211.2252   $1,211.22   $1,211.25   $1,211.20