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	$52.42	5.198%	$55.1448	$55.14	$55.15	$55.10
Purchase #2	$103.58	12.511%	$116.5389	$116.54	$116.55	$116.50
Purchase #3	$45.83	7.203%	$49.1311	$49.13	$49.15	$49.10
Purchase #4	$147.86	7.272%	$158.6124	$158.61	$158.60	$158.60
Purchase #5	$188.67	9.391%	$206.388	$206.39	$206.40	$206.40
Purchase #6	$185.32	10.567%	$204.9028	$204.90	$204.90	$204.90
Purchase #7	$94.92	5.870%	$100.4918	$100.49	$100.50	$100.50
7 purchase totals =	$818.60		$891.2098	$891.20	$891.25	$891.10