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	$200.70	12.466%	$225.7193	$225.72	$225.70	$225.70
Purchase #2	$52.56	5.636%	$55.5223	$55.52	$55.50	$55.50
Purchase #3	$83.70	6.751%	$89.3506	$89.35	$89.35	$89.40
Purchase #4	$72.81	9.149%	$79.4714	$79.47	$79.45	$79.50
Purchase #5	$58.72	13.262%	$66.5074	$66.51	$66.50	$66.50
Purchase #6	$53.38	13.427%	$60.5473	$60.55	$60.55	$60.50
Purchase #7	$44.73	13.314%	$50.6854	$50.69	$50.70	$50.70
7 purchase totals =	$566.60		$627.8037	$627.81	$627.75	$627.80