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	$172.77	7.368%	$185.4997	$185.50	$185.50	$185.50
Purchase #2	$231.80	10.386%	$255.8747	$255.87	$255.85	$255.90
Purchase #3	$99.27	12.504%	$111.6827	$111.68	$111.70	$111.70
Purchase #4	$169.49	3.774%	$175.8866	$175.89	$175.90	$175.90
Purchase #5	$96.64	12.227%	$108.4562	$108.46	$108.45	$108.50
Purchase #6	$37.42	10.139%	$41.214	$41.21	$41.20	$41.20
Purchase #7	$89.54	6.859%	$95.6815	$95.68	$95.70	$95.70
7 purchase totals =	$896.93		$974.2954	$974.29	$974.30	$974.40