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	$20.38	10.488%	$22.5175	$22.52	$22.50	$22.50
Purchase #2	$30.28	7.737%	$32.6228	$32.62	$32.60	$32.60
Purchase #3	$230.52	12.631%	$259.637	$259.64	$259.65	$259.60
Purchase #4	$175.37	9.220%	$191.5391	$191.54	$191.55	$191.50
Purchase #5	$138.58	9.303%	$151.4721	$151.47	$151.45	$151.50
Purchase #6	$172.31	12.835%	$194.426	$194.43	$194.45	$194.40
Purchase #7	$111.38	6.607%	$118.7389	$118.74	$118.75	$118.70
7 purchase totals =	$878.82		$970.9534	$970.96	$970.95	$970.80