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 $65.58   12.853%   $74.009   $74.01   $74.00   $74.00  
  Purchase #2 $140.67   8.556%   $152.7057   $152.71   $152.70   $152.70  
  Purchase #3 $101.90   12.299%   $114.4327   $114.43   $114.45   $114.40  
  Purchase #4 $211.85   12.281%   $237.8673   $237.87   $237.85   $237.90  
  Purchase #5 $138.70   11.388%   $154.4952   $154.50   $154.50   $154.50  
  Purchase #6 $5.41   12.626%   $6.0931   $6.09   $6.10   $6.10  
  Purchase #7 $40.83   3.211%   $42.1411   $42.14   $42.15   $42.10  
  7 purchase totals = $704.94       $781.7441   $781.75   $781.75   $781.70