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 $208.86   6.320%   $222.06   $222.06   $222.05   $222.10  
  Purchase #2 $74.73   3.244%   $77.1542   $77.15   $77.15   $77.20  
  Purchase #3 $176.26   9.457%   $192.9289   $192.93   $192.95   $192.90  
  Purchase #4 $59.95   7.456%   $64.4199   $64.42   $64.40   $64.40  
  Purchase #5 $146.72   12.345%   $164.8326   $164.83   $164.85   $164.80  
  Purchase #6 $44.82   8.313%   $48.5459   $48.55   $48.55   $48.50  
  Purchase #7 $156.42   10.865%   $173.415   $173.42   $173.40   $173.40  
  7 purchase totals = $867.76       $943.3565   $943.36   $943.35   $943.30