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	$210.34	9.543%	$230.4127	$230.41	$230.40	$230.40
Purchase #2	$143.28	5.605%	$151.3108	$151.31	$151.30	$151.30
Purchase #3	$176.52	13.409%	$200.1896	$200.19	$200.20	$200.20
Purchase #4	$102.29	3.449%	$105.818	$105.82	$105.80	$105.80
Purchase #5	$50.79	9.456%	$55.5927	$55.59	$55.60	$55.60
Purchase #6	$86.53	10.386%	$95.517	$95.52	$95.50	$95.50
Purchase #7	$58.83	13.379%	$66.7009	$66.70	$66.70	$66.70
7 purchase totals =	$828.58		$905.5417	$905.54	$905.50	$905.50