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 $246.37   9.209%   $269.0582   $269.06   $269.05   $269.10  
  Purchase #2 $32.73   6.267%   $34.7812   $34.78   $34.80   $34.80  
  Purchase #3 $51.48   7.582%   $55.3832   $55.38   $55.40   $55.40  
  Purchase #4 $25.86   7.713%   $27.8546   $27.85   $27.85   $27.90  
  Purchase #5 $104.77   8.664%   $113.8473   $113.85   $113.85   $113.80  
  Purchase #6 $36.61   4.299%   $38.1839   $38.18   $38.20   $38.20  
  Purchase #7 $206.97   9.825%   $227.3048   $227.30   $227.30   $227.30  
  7 purchase totals = $704.79       $766.4132   $766.40   $766.45   $766.50