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	$88.53	13.332%	$100.3328	$100.33	$100.35	$100.30
Purchase #2	$57.33	3.143%	$59.1319	$59.13	$59.15	$59.10
Purchase #3	$59.45	11.689%	$66.3991	$66.40	$66.40	$66.40
Purchase #4	$138.31	9.660%	$151.6707	$151.67	$151.65	$151.70
Purchase #5	$36.64	9.823%	$40.2391	$40.24	$40.25	$40.20
Purchase #6	$217.30	8.383%	$235.5163	$235.52	$235.50	$235.50
Purchase #7	$52.36	4.576%	$54.756	$54.76	$54.75	$54.80
7 purchase totals =	$649.92		$708.0459	$708.05	$708.05	$708.00