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	$143.54	5.328%	$151.1878	$151.19	$151.20	$151.20
Purchase #2	$70.70	11.286%	$78.6792	$78.68	$78.70	$78.70
Purchase #3	$241.28	12.801%	$272.1663	$272.17	$272.15	$272.20
Purchase #4	$35.84	5.191%	$37.7005	$37.70	$37.70	$37.70
Purchase #5	$28.74	9.640%	$31.5105	$31.51	$31.50	$31.50
Purchase #6	$139.71	11.141%	$155.2751	$155.28	$155.30	$155.30
Purchase #7	$65.72	6.516%	$70.0023	$70.00	$70.00	$70.00
7 purchase totals =	$725.53		$796.5217	$796.53	$796.55	$796.60