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 $217.68   12.364%   $244.594   $244.59   $244.60   $244.60  
  Purchase #2 $88.68   4.663%   $92.8151   $92.82   $92.80   $92.80  
  Purchase #3 $65.34   3.705%   $67.7608   $67.76   $67.75   $67.80  
  Purchase #4 $242.49   3.138%   $250.0993   $250.10   $250.10   $250.10  
  Purchase #5 $186.83   4.537%   $195.3065   $195.31   $195.30   $195.30  
  Purchase #6 $250.83   10.364%   $276.826   $276.83   $276.85   $276.80  
  Purchase #7 $235.58   3.429%   $243.658   $243.66   $243.65   $243.70  
  7 purchase totals = $1,287.43       $1,371.0597   $1,371.07   $1,371.05   $1,371.10