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 $11.85   13.812%   $13.4867   $13.49   $13.50   $13.50  
  Purchase #2 $232.49   9.565%   $254.7277   $254.73   $254.75   $254.70  
  Purchase #3 $51.62   9.831%   $56.6948   $56.69   $56.70   $56.70  
  Purchase #4 $41.99   5.178%   $44.1642   $44.16   $44.15   $44.20  
  Purchase #5 $64.75   13.324%   $73.3773   $73.38   $73.40   $73.40  
  Purchase #6 $136.56   3.461%   $141.2863   $141.29   $141.30   $141.30  
  Purchase #7 $224.45   6.630%   $239.331   $239.33   $239.35   $239.30  
  7 purchase totals = $763.71       $823.0680   $823.07   $823.15   $823.10