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	$198.83	12.466%	$223.6161	$223.62	$223.60	$223.60
Purchase #2	$88.65	13.726%	$100.8181	$100.82	$100.80	$100.80
Purchase #3	$132.26	3.339%	$136.6762	$136.68	$136.70	$136.70
Purchase #4	$229.94	10.735%	$254.6241	$254.62	$254.60	$254.60
Purchase #5	$124.46	6.111%	$132.0658	$132.07	$132.05	$132.10
Purchase #6	$123.65	7.122%	$132.4564	$132.46	$132.45	$132.50
Purchase #7	$217.39	7.428%	$233.5377	$233.54	$233.55	$233.50
7 purchase totals =	$1,115.18		$1,213.7944	$1,213.81	$1,213.75	$1,213.80