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	$215.45	4.672%	$225.5158	$225.52	$225.50	$225.50
Purchase #2	$186.69	10.703%	$206.6714	$206.67	$206.65	$206.70
Purchase #3	$222.55	7.116%	$238.3867	$238.39	$238.40	$238.40
Purchase #4	$90.59	9.695%	$99.3727	$99.37	$99.35	$99.40
Purchase #5	$62.97	5.417%	$66.3811	$66.38	$66.40	$66.40
Purchase #6	$190.71	12.308%	$214.1826	$214.18	$214.20	$214.20
Purchase #7	$68.94	3.203%	$71.1481	$71.15	$71.15	$71.10
7 purchase totals =	$1,037.90		$1,121.6584	$1,121.66	$1,121.65	$1,121.70