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 $125.41   4.454%   $130.9958   $131.00   $131.00   $131.00  
  Purchase #2 $47.69   3.387%   $49.3053   $49.31   $49.30   $49.30  
  Purchase #3 $91.63   7.747%   $98.7286   $98.73   $98.75   $98.70  
  Purchase #4 $58.84   3.593%   $60.9541   $60.95   $60.95   $61.00  
  Purchase #5 $76.90   7.335%   $82.5406   $82.54   $82.55   $82.50  
  Purchase #6 $102.39   11.867%   $114.5406   $114.54   $114.55   $114.50  
  Purchase #7 $235.56   4.426%   $245.9859   $245.99   $246.00   $246.00  
  7 purchase totals = $738.42       $783.0509   $783.06   $783.10   $783.00