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 $188.77   8.679%   $205.1533   $205.15   $205.15   $205.20  
  Purchase #2 $250.58   11.785%   $280.1109   $280.11   $280.10   $280.10  
  Purchase #3 $113.38   8.105%   $122.5694   $122.57   $122.55   $122.60  
  Purchase #4 $73.67   3.570%   $76.3   $76.30   $76.30   $76.30  
  Purchase #5 $61.57   5.489%   $64.9496   $64.95   $64.95   $64.90  
  Purchase #6 $97.45   8.674%   $105.9028   $105.90   $105.90   $105.90  
  Purchase #7 $249.62   12.703%   $281.3292   $281.33   $281.35   $281.30  
  7 purchase totals = $1,035.04       $1,136.3152   $1,136.31   $1,136.30   $1,136.30