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	$146.89	10.505%	$162.3208	$162.32	$162.30	$162.30
Purchase #2	$74.94	11.539%	$83.5873	$83.59	$83.60	$83.60
Purchase #3	$172.62	3.725%	$179.0501	$179.05	$179.05	$179.10
Purchase #4	$95.71	9.201%	$104.5163	$104.52	$104.50	$104.50
Purchase #5	$6.28	11.117%	$6.9781	$6.98	$7.00	$7.00
Purchase #6	$152.47	4.289%	$159.0094	$159.01	$159.00	$159.00
Purchase #7	$92.84	13.195%	$105.0902	$105.09	$105.10	$105.10
7 purchase totals =	$741.75		$800.5522	$800.56	$800.55	$800.60