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	$17.30	7.127%	$18.533	$18.53	$18.55	$18.50
Purchase #2	$151.47	12.576%	$170.5189	$170.52	$170.50	$170.50
Purchase #3	$95.79	10.130%	$105.4935	$105.49	$105.50	$105.50
Purchase #4	$170.38	8.488%	$184.8419	$184.84	$184.85	$184.80
Purchase #5	$111.27	6.314%	$118.2956	$118.30	$118.30	$118.30
Purchase #6	$248.71	10.845%	$275.6826	$275.68	$275.70	$275.70
Purchase #7	$20.42	4.145%	$21.2664	$21.27	$21.25	$21.30
7 purchase totals =	$815.34		$894.6319	$894.63	$894.65	$894.60