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 $59.60   11.628%   $66.5303   $66.53   $66.55   $66.50  
  Purchase #2 $104.89   9.449%   $114.8011   $114.80   $114.80   $114.80  
  Purchase #3 $45.98   8.306%   $49.7991   $49.80   $49.80   $49.80  
  Purchase #4 $137.27   3.332%   $141.8438   $141.84   $141.85   $141.80  
  Purchase #5 $154.63   4.790%   $162.0368   $162.04   $162.05   $162.00  
  Purchase #6 $128.72   12.460%   $144.7585   $144.76   $144.75   $144.80  
  Purchase #7 $86.48   5.579%   $91.3047   $91.30   $91.30   $91.30  
  7 purchase totals = $717.57       $771.0743   $771.07   $771.10   $771.00