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	$105.32	10.352%	$116.2227	$116.22	$116.20	$116.20
Purchase #2	$175.50	12.130%	$196.7882	$196.79	$196.80	$196.80
Purchase #3	$28.25	13.290%	$32.0044	$32.00	$32.00	$32.00
Purchase #4	$168.41	6.557%	$179.4526	$179.45	$179.45	$179.50
Purchase #5	$111.32	4.624%	$116.4674	$116.47	$116.45	$116.50
Purchase #6	$32.76	5.559%	$34.5811	$34.58	$34.60	$34.60
Purchase #7	$154.50	3.309%	$159.6124	$159.61	$159.60	$159.60
7 purchase totals =	$776.06		$835.1288	$835.12	$835.10	$835.20