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	$36.35	13.291%	$41.1813	$41.18	$41.20	$41.20
Purchase #2	$177.58	6.287%	$188.7445	$188.74	$188.75	$188.70
Purchase #3	$160.97	7.267%	$172.6677	$172.67	$172.65	$172.70
Purchase #4	$81.54	9.230%	$89.0661	$89.07	$89.05	$89.10
Purchase #5	$47.32	12.810%	$53.3817	$53.38	$53.40	$53.40
Purchase #6	$117.50	11.160%	$130.613	$130.61	$130.60	$130.60
Purchase #7	$111.69	5.752%	$118.1144	$118.11	$118.10	$118.10
7 purchase totals =	$732.95		$793.7687	$793.76	$793.75	$793.80