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	$175.32	7.785%	$188.9687	$188.97	$188.95	$189.00
Purchase #2	$116.42	9.541%	$127.5276	$127.53	$127.55	$127.50
Purchase #3	$145.52	9.429%	$159.2411	$159.24	$159.25	$159.20
Purchase #4	$28.72	13.293%	$32.5377	$32.54	$32.55	$32.50
Purchase #5	$47.89	9.462%	$52.4214	$52.42	$52.40	$52.40
Purchase #6	$51.93	11.158%	$57.7243	$57.72	$57.70	$57.70
Purchase #7	$47.90	10.826%	$53.0857	$53.09	$53.10	$53.10
7 purchase totals =	$613.70		$671.5065	$671.51	$671.50	$671.40