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 $215.92   8.265%   $233.7658   $233.77   $233.75   $233.80  
  Purchase #2 $194.32   7.484%   $208.8629   $208.86   $208.85   $208.90  
  Purchase #3 $115.61   7.797%   $124.6241   $124.62   $124.60   $124.60  
  Purchase #4 $114.70   4.118%   $119.4233   $119.42   $119.40   $119.40  
  Purchase #5 $25.60   3.712%   $26.5503   $26.55   $26.55   $26.60  
  Purchase #6 $247.36   5.245%   $260.334   $260.33   $260.35   $260.30  
  Purchase #7 $131.76   3.354%   $136.1792   $136.18   $136.20   $136.20  
  7 purchase totals = $1,045.27       $1,109.7396   $1,109.73   $1,109.70   $1,109.80