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	$44.73	7.738%	$48.1912	$48.19	$48.20	$48.20
Purchase #2	$233.28	6.543%	$248.5435	$248.54	$248.55	$248.50
Purchase #3	$238.57	8.102%	$257.8989	$257.90	$257.90	$257.90
Purchase #4	$210.91	11.600%	$235.3756	$235.38	$235.40	$235.40
Purchase #5	$83.90	6.581%	$89.4215	$89.42	$89.40	$89.40
Purchase #6	$117.60	13.624%	$133.6218	$133.62	$133.60	$133.60
Purchase #7	$148.83	4.748%	$155.8964	$155.90	$155.90	$155.90
7 purchase totals =	$1,077.82		$1,168.9489	$1,168.95	$1,168.95	$1,168.90