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 $206.29   11.776%   $230.5827   $230.58   $230.60   $230.60  
  Purchase #2 $148.98   8.400%   $161.4943   $161.49   $161.50   $161.50  
  Purchase #3 $224.25   8.105%   $242.4255   $242.43   $242.45   $242.40  
  Purchase #4 $121.67   7.150%   $130.3694   $130.37   $130.35   $130.40  
  Purchase #5 $96.53   6.542%   $102.845   $102.85   $102.85   $102.80  
  Purchase #6 $61.85   4.587%   $64.6871   $64.69   $64.70   $64.70  
  Purchase #7 $132.78   3.393%   $137.2852   $137.29   $137.30   $137.30  
  7 purchase totals = $992.35       $1,069.6892   $1,069.70   $1,069.75   $1,069.70