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	$248.47	9.527%	$272.1417	$272.14	$272.15	$272.10
Purchase #2	$70.75	11.385%	$78.8049	$78.80	$78.80	$78.80
Purchase #3	$143.27	8.364%	$155.2531	$155.25	$155.25	$155.30
Purchase #4	$48.86	10.537%	$54.0084	$54.01	$54.00	$54.00
Purchase #5	$198.47	3.607%	$205.6288	$205.63	$205.65	$205.60
Purchase #6	$179.40	10.822%	$198.8147	$198.81	$198.80	$198.80
Purchase #7	$6.40	13.804%	$7.2835	$7.28	$7.30	$7.30
7 purchase totals =	$895.62		$971.9351	$971.92	$971.95	$971.90