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	$248.36	3.130%	$256.1337	$256.13	$256.15	$256.10
Purchase #2	$120.88	6.525%	$128.7674	$128.77	$128.75	$128.80
Purchase #3	$19.62	7.722%	$21.1351	$21.14	$21.15	$21.10
Purchase #4	$243.28	5.299%	$256.1714	$256.17	$256.15	$256.20
Purchase #5	$151.99	13.605%	$172.6682	$172.67	$172.65	$172.70
Purchase #6	$83.73	8.851%	$91.1409	$91.14	$91.15	$91.10
Purchase #7	$129.53	9.753%	$142.1631	$142.16	$142.15	$142.20
7 purchase totals =	$997.39		$1,068.1798	$1,068.18	$1,068.15	$1,068.20