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	$54.65	11.594%	$60.9861	$60.99	$61.00	$61.00
Purchase #2	$69.58	12.546%	$78.3095	$78.31	$78.30	$78.30
Purchase #3	$152.94	9.190%	$166.9952	$167.00	$167.00	$167.00
Purchase #4	$42.42	6.204%	$45.0517	$45.05	$45.05	$45.10
Purchase #5	$121.72	10.634%	$134.6637	$134.66	$134.65	$134.70
Purchase #6	$103.91	7.690%	$111.9007	$111.90	$111.90	$111.90
Purchase #7	$184.49	13.394%	$209.2006	$209.20	$209.20	$209.20
7 purchase totals =	$729.71		$807.1075	$807.11	$807.10	$807.20