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	$111.82	6.325%	$118.8926	$118.89	$118.90	$118.90
Purchase #2	$205.96	5.259%	$216.7914	$216.79	$216.80	$216.80
Purchase #3	$30.89	6.379%	$32.8605	$32.86	$32.85	$32.90
Purchase #4	$211.78	10.294%	$233.5806	$233.58	$233.60	$233.60
Purchase #5	$212.34	12.686%	$239.2775	$239.28	$239.30	$239.30
Purchase #6	$158.82	7.597%	$170.8856	$170.89	$170.90	$170.90
Purchase #7	$108.86	8.514%	$118.1283	$118.13	$118.15	$118.10
7 purchase totals =	$1,040.47		$1,130.4165	$1,130.42	$1,130.50	$1,130.50