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 $218.38   12.157%   $244.9285   $244.93   $244.95   $244.90  
  Purchase #2 $93.71   8.523%   $101.6969   $101.70   $101.70   $101.70  
  Purchase #3 $71.55   11.422%   $79.7224   $79.72   $79.70   $79.70  
  Purchase #4 $56.50   12.426%   $63.5207   $63.52   $63.50   $63.50  
  Purchase #5 $234.69   10.669%   $259.7291   $259.73   $259.75   $259.70  
  Purchase #6 $233.33   11.410%   $259.953   $259.95   $259.95   $260.00  
  Purchase #7 $194.87   13.600%   $221.3723   $221.37   $221.35   $221.40  
  7 purchase totals = $1,103.03       $1,230.9229   $1,230.92   $1,230.90   $1,230.90