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	$29.78	6.114%	$31.6007	$31.60	$31.60	$31.60
Purchase #2	$233.34	12.580%	$262.6942	$262.69	$262.70	$262.70
Purchase #3	$6.87	3.461%	$7.1078	$7.11	$7.10	$7.10
Purchase #4	$112.59	13.419%	$127.6985	$127.70	$127.70	$127.70
Purchase #5	$174.40	11.668%	$194.749	$194.75	$194.75	$194.70
Purchase #6	$10.84	3.810%	$11.253	$11.25	$11.25	$11.30
Purchase #7	$23.95	13.635%	$27.2156	$27.22	$27.20	$27.20
7 purchase totals =	$591.77		$662.3188	$662.32	$662.30	$662.30