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	$129.83	10.559%	$143.5387	$143.54	$143.55	$143.50
Purchase #2	$65.42	8.721%	$71.1253	$71.13	$71.15	$71.10
Purchase #3	$47.90	12.608%	$53.9392	$53.94	$53.95	$53.90
Purchase #4	$59.25	5.505%	$62.5117	$62.51	$62.50	$62.50
Purchase #5	$91.55	8.478%	$99.3116	$99.31	$99.30	$99.30
Purchase #6	$41.60	3.367%	$43.0007	$43.00	$43.00	$43.00
Purchase #7	$53.26	7.495%	$57.2518	$57.25	$57.25	$57.30
7 purchase totals =	$488.81		$530.6790	$530.68	$530.70	$530.60