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	$117.28	9.435%	$128.3454	$128.35	$128.35	$128.30
Purchase #2	$244.82	12.864%	$276.3136	$276.31	$276.30	$276.30
Purchase #3	$215.66	4.551%	$225.4747	$225.47	$225.45	$225.50
Purchase #4	$184.65	4.600%	$193.1439	$193.14	$193.15	$193.10
Purchase #5	$172.69	7.227%	$185.1703	$185.17	$185.15	$185.20
Purchase #6	$106.59	11.579%	$118.9321	$118.93	$118.95	$118.90
Purchase #7	$191.71	10.332%	$211.5175	$211.52	$211.50	$211.50
7 purchase totals =	$1,233.40		$1,338.8975	$1,338.89	$1,338.85	$1,338.80