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 $217.48   12.444%   $244.5432   $244.54   $244.55   $244.50  
  Purchase #2 $51.34   6.552%   $54.7038   $54.70   $54.70   $54.70  
  Purchase #3 $247.68   3.559%   $256.4949   $256.49   $256.50   $256.50  
  Purchase #4 $94.80   3.852%   $98.4517   $98.45   $98.45   $98.50  
  Purchase #5 $11.47   4.697%   $12.0087   $12.01   $12.00   $12.00  
  Purchase #6 $96.90   8.282%   $104.9253   $104.93   $104.95   $104.90  
  Purchase #7 $231.44   13.482%   $262.6427   $262.64   $262.65   $262.60  
  7 purchase totals = $951.11       $1,033.7703   $1,033.76   $1,033.80   $1,033.70