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 $226.71   9.102%   $247.3451   $247.35   $247.35   $247.30  
  Purchase #2 $208.38   6.492%   $221.908   $221.91   $221.90   $221.90  
  Purchase #3 $126.39   3.239%   $130.4838   $130.48   $130.50   $130.50  
  Purchase #4 $166.57   4.425%   $173.9407   $173.94   $173.95   $173.90  
  Purchase #5 $64.90   13.314%   $73.5408   $73.54   $73.55   $73.50  
  Purchase #6 $204.26   5.266%   $215.0163   $215.02   $215.00   $215.00  
  Purchase #7 $119.85   10.466%   $132.3935   $132.39   $132.40   $132.40  
  7 purchase totals = $1,117.06       $1,194.6282   $1,194.63   $1,194.65   $1,194.50