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 $219.70   8.621%   $238.6403   $238.64   $238.65   $238.60  
  Purchase #2 $236.51   13.192%   $267.7104   $267.71   $267.70   $267.70  
  Purchase #3 $179.49   7.510%   $192.9697   $192.97   $192.95   $193.00  
  Purchase #4 $77.92   6.583%   $83.0495   $83.05   $83.05   $83.00  
  Purchase #5 $246.53   5.484%   $260.0497   $260.05   $260.05   $260.00  
  Purchase #6 $57.55   10.692%   $63.7032   $63.70   $63.70   $63.70  
  Purchase #7 $224.62   8.639%   $244.0249   $244.02   $244.00   $244.00  
  7 purchase totals = $1,242.32       $1,350.1477   $1,350.14   $1,350.10   $1,350.00