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	$151.85	13.377%	$172.163	$172.16	$172.15	$172.20
Purchase #2	$148.32	12.352%	$166.6405	$166.64	$166.65	$166.60
Purchase #3	$170.42	10.510%	$188.3311	$188.33	$188.35	$188.30
Purchase #4	$239.56	11.135%	$266.235	$266.24	$266.25	$266.20
Purchase #5	$90.68	10.447%	$100.1533	$100.15	$100.15	$100.20
Purchase #6	$34.54	7.461%	$37.117	$37.12	$37.10	$37.10
Purchase #7	$94.25	5.429%	$99.3668	$99.37	$99.35	$99.40
7 purchase totals =	$929.62		$1,030.0067	$1,030.01	$1,030.00	$1,030.00