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 $182.34   12.298%   $204.7642   $204.76   $204.75   $204.80  
  Purchase #2 $30.27   3.733%   $31.4   $31.40   $31.40   $31.40  
  Purchase #3 $64.74   4.838%   $67.8721   $67.87   $67.85   $67.90  
  Purchase #4 $5.37   9.786%   $5.8955   $5.90   $5.90   $5.90  
  Purchase #5 $115.97   8.635%   $125.984   $125.98   $126.00   $126.00  
  Purchase #6 $176.88   8.822%   $192.4844   $192.48   $192.50   $192.50  
  Purchase #7 $22.26   8.678%   $24.1917   $24.19   $24.20   $24.20  
  7 purchase totals = $597.83       $652.5919   $652.58   $652.60   $652.70