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 $224.96   4.804%   $235.7671   $235.77   $235.75   $235.80  
  Purchase #2 $69.31   10.468%   $76.5654   $76.57   $76.55   $76.60  
  Purchase #3 $216.45   5.335%   $227.9976   $228.00   $228.00   $228.00  
  Purchase #4 $124.26   12.343%   $139.5974   $139.60   $139.60   $139.60  
  Purchase #5 $5.54   13.762%   $6.3024   $6.30   $6.30   $6.30  
  Purchase #6 $237.82   6.732%   $253.83   $253.83   $253.85   $253.80  
  Purchase #7 $207.30   12.143%   $232.4724   $232.47   $232.45   $232.50  
  7 purchase totals = $1,085.64       $1,172.5323   $1,172.54   $1,172.50   $1,172.60