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	$125.83	5.819%	$133.152	$133.15	$133.15	$133.20
Purchase #2	$225.56	13.837%	$256.7707	$256.77	$256.75	$256.80
Purchase #3	$143.43	4.694%	$150.1626	$150.16	$150.15	$150.20
Purchase #4	$158.91	13.204%	$179.8925	$179.89	$179.90	$179.90
Purchase #5	$153.31	3.845%	$159.2048	$159.20	$159.20	$159.20
Purchase #6	$47.83	11.469%	$53.3156	$53.32	$53.30	$53.30
Purchase #7	$51.69	7.736%	$55.6887	$55.69	$55.70	$55.70
7 purchase totals =	$906.56		$988.1869	$988.18	$988.15	$988.30