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 $219.85   11.255%   $244.5941   $244.59   $244.60   $244.60  
  Purchase #2 $188.54   11.645%   $210.4955   $210.50   $210.50   $210.50  
  Purchase #3 $34.64   12.707%   $39.0417   $39.04   $39.05   $39.00  
  Purchase #4 $243.47   7.492%   $261.7108   $261.71   $261.70   $261.70  
  Purchase #5 $178.63   7.485%   $192.0005   $192.00   $192.00   $192.00  
  Purchase #6 $87.83   9.620%   $96.2792   $96.28   $96.30   $96.30  
  Purchase #7 $181.67   10.313%   $200.4056   $200.41   $200.40   $200.40  
  7 purchase totals = $1,134.63       $1,244.5274   $1,244.53   $1,244.55   $1,244.50