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 $101.36   13.271%   $114.8115   $114.81   $114.80   $114.80  
  Purchase #2 $247.53   9.635%   $271.3795   $271.38   $271.40   $271.40  
  Purchase #3 $224.40   7.396%   $240.9966   $241.00   $241.00   $241.00  
  Purchase #4 $90.87   3.795%   $94.3185   $94.32   $94.30   $94.30  
  Purchase #5 $211.71   8.278%   $229.2354   $229.24   $229.25   $229.20  
  Purchase #6 $59.34   8.566%   $64.4231   $64.42   $64.40   $64.40  
  Purchase #7 $32.85   13.429%   $37.2614   $37.26   $37.25   $37.30  
  7 purchase totals = $968.06       $1,052.4260   $1,052.43   $1,052.40   $1,052.40