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 $197.76   3.263%   $204.2129   $204.21   $204.20   $204.20  
  Purchase #2 $96.82   7.308%   $103.8956   $103.90   $103.90   $103.90  
  Purchase #3 $215.94   5.439%   $227.685   $227.69   $227.70   $227.70  
  Purchase #4 $132.62   6.428%   $141.1448   $141.14   $141.15   $141.10  
  Purchase #5 $163.50   11.755%   $182.7194   $182.72   $182.70   $182.70  
  Purchase #6 $28.58   4.131%   $29.7606   $29.76   $29.75   $29.80  
  Purchase #7 $56.84   4.592%   $59.4501   $59.45   $59.45   $59.50  
  7 purchase totals = $892.06       $948.8684   $948.87   $948.85   $948.90