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	$121.70	5.679%	$128.6113	$128.61	$128.60	$128.60
Purchase #2	$70.59	11.676%	$78.8321	$78.83	$78.85	$78.80
Purchase #3	$141.33	8.177%	$152.8866	$152.89	$152.90	$152.90
Purchase #4	$71.99	6.388%	$76.5887	$76.59	$76.60	$76.60
Purchase #5	$68.87	4.784%	$72.1647	$72.16	$72.15	$72.20
Purchase #6	$111.63	13.760%	$126.9903	$126.99	$127.00	$127.00
Purchase #7	$34.73	10.258%	$38.2926	$38.29	$38.30	$38.30
7 purchase totals =	$620.84		$674.3663	$674.36	$674.40	$674.40