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 $89.67   6.149%   $95.1838   $95.18   $95.20   $95.20  
  Purchase #2 $121.78   3.706%   $126.2932   $126.29   $126.30   $126.30  
  Purchase #3 $176.47   13.226%   $199.8099   $199.81   $199.80   $199.80  
  Purchase #4 $22.76   10.165%   $25.0736   $25.07   $25.05   $25.10  
  Purchase #5 $209.58   8.710%   $227.8344   $227.83   $227.85   $227.80  
  Purchase #6 $60.31   11.697%   $67.3645   $67.36   $67.35   $67.40  
  Purchase #7 $202.76   7.310%   $217.5818   $217.58   $217.60   $217.60  
  7 purchase totals = $883.33       $959.1412   $959.12   $959.15   $959.20