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 $63.87   3.863%   $66.3373   $66.34   $66.35   $66.30  
  Purchase #2 $59.39   3.545%   $61.4954   $61.50   $61.50   $61.50  
  Purchase #3 $194.26   6.214%   $206.3313   $206.33   $206.35   $206.30  
  Purchase #4 $222.25   3.440%   $229.8954   $229.90   $229.90   $229.90  
  Purchase #5 $146.30   5.515%   $154.3684   $154.37   $154.35   $154.40  
  Purchase #6 $207.53   12.691%   $233.8676   $233.87   $233.85   $233.90  
  Purchase #7 $64.93   13.602%   $73.7618   $73.76   $73.75   $73.80  
  7 purchase totals = $958.53       $1,026.0572   $1,026.07   $1,026.05   $1,026.10