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	$25.61	11.214%	$28.4819	$28.48	$28.50	$28.50
Purchase #2	$48.95	13.453%	$55.5352	$55.54	$55.55	$55.50
Purchase #3	$77.28	6.828%	$82.5567	$82.56	$82.55	$82.60
Purchase #4	$216.72	4.812%	$227.1486	$227.15	$227.15	$227.10
Purchase #5	$192.45	7.801%	$207.463	$207.46	$207.45	$207.50
Purchase #6	$65.40	11.130%	$72.679	$72.68	$72.70	$72.70
Purchase #7	$124.57	5.613%	$131.5621	$131.56	$131.55	$131.60
7 purchase totals =	$750.98		$805.4265	$805.43	$805.45	$805.50