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 $173.71   12.119%   $194.7619   $194.76   $194.75   $194.80  
  Purchase #2 $168.54   8.844%   $183.4457   $183.45   $183.45   $183.40  
  Purchase #3 $190.64   11.864%   $213.2575   $213.26   $213.25   $213.30  
  Purchase #4 $105.78   8.428%   $114.6951   $114.70   $114.70   $114.70  
  Purchase #5 $36.83   9.347%   $40.2725   $40.27   $40.25   $40.30  
  Purchase #6 $247.85   7.221%   $265.7472   $265.75   $265.75   $265.70  
  Purchase #7 $64.91   11.757%   $72.5415   $72.54   $72.55   $72.50  
  7 purchase totals = $988.26       $1,084.7214   $1,084.73   $1,084.70   $1,084.70