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	$46.51	8.174%	$50.3117	$50.31	$50.30	$50.30
Purchase #2	$193.62	6.752%	$206.6932	$206.69	$206.70	$206.70
Purchase #3	$81.45	10.213%	$89.7685	$89.77	$89.75	$89.80
Purchase #4	$229.75	9.240%	$250.9789	$250.98	$251.00	$251.00
Purchase #5	$41.69	9.198%	$45.5246	$45.52	$45.50	$45.50
Purchase #6	$48.64	13.231%	$55.0756	$55.08	$55.10	$55.10
Purchase #7	$169.37	6.130%	$179.7524	$179.75	$179.75	$179.80
7 purchase totals =	$811.03		$878.1049	$878.10	$878.10	$878.20