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	$50.66	5.642%	$53.5182	$53.52	$53.50	$53.50
Purchase #2	$30.66	6.501%	$32.6532	$32.65	$32.65	$32.70
Purchase #3	$162.48	13.720%	$184.7723	$184.77	$184.75	$184.80
Purchase #4	$216.92	10.600%	$239.9135	$239.91	$239.90	$239.90
Purchase #5	$228.72	4.158%	$238.2302	$238.23	$238.25	$238.20
Purchase #6	$148.84	11.748%	$166.3257	$166.33	$166.35	$166.30
Purchase #7	$145.34	7.549%	$156.3117	$156.31	$156.30	$156.30
7 purchase totals =	$983.62		$1,071.7248	$1,071.72	$1,071.70	$1,071.70