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	$79.87	12.816%	$90.1061	$90.11	$90.10	$90.10
Purchase #2	$125.56	10.376%	$138.5881	$138.59	$138.60	$138.60
Purchase #3	$194.42	4.679%	$203.5169	$203.52	$203.50	$203.50
Purchase #4	$130.73	12.332%	$146.8516	$146.85	$146.85	$146.90
Purchase #5	$97.98	13.728%	$111.4307	$111.43	$111.45	$111.40
Purchase #6	$91.98	9.485%	$100.7043	$100.70	$100.70	$100.70
Purchase #7	$245.27	12.114%	$274.982	$274.98	$275.00	$275.00
7 purchase totals =	$965.81		$1,066.1797	$1,066.18	$1,066.20	$1,066.20