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	$9.60	5.776%	$10.1545	$10.15	$10.15	$10.20
Purchase #2	$95.61	4.261%	$99.6839	$99.68	$99.70	$99.70
Purchase #3	$216.31	11.728%	$241.6788	$241.68	$241.70	$241.70
Purchase #4	$133.68	12.684%	$150.636	$150.64	$150.65	$150.60
Purchase #5	$158.77	4.690%	$166.2163	$166.22	$166.20	$166.20
Purchase #6	$242.25	10.153%	$266.8456	$266.85	$266.85	$266.80
Purchase #7	$69.72	5.117%	$73.2876	$73.29	$73.30	$73.30
7 purchase totals =	$925.94		$1,008.5027	$1,008.51	$1,008.55	$1,008.50