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	$100.33	12.660%	$113.0318	$113.03	$113.05	$113.00
Purchase #2	$132.50	10.262%	$146.0972	$146.10	$146.10	$146.10
Purchase #3	$64.89	3.149%	$66.9334	$66.93	$66.95	$66.90
Purchase #4	$54.63	6.874%	$58.3853	$58.39	$58.40	$58.40
Purchase #5	$74.49	10.865%	$82.5833	$82.58	$82.60	$82.60
Purchase #6	$156.60	5.738%	$165.5857	$165.59	$165.60	$165.60
Purchase #7	$54.85	4.230%	$57.1702	$57.17	$57.15	$57.20
7 purchase totals =	$638.29		$689.7869	$689.79	$689.85	$689.80