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	$102.27	10.626%	$113.1372	$113.14	$113.15	$113.10
Purchase #2	$229.68	8.845%	$249.9952	$250.00	$250.00	$250.00
Purchase #3	$133.65	11.363%	$148.8366	$148.84	$148.85	$148.80
Purchase #4	$77.69	11.341%	$86.5008	$86.50	$86.50	$86.50
Purchase #5	$154.29	13.761%	$175.5218	$175.52	$175.50	$175.50
Purchase #6	$54.90	11.729%	$61.3392	$61.34	$61.35	$61.30
Purchase #7	$153.45	12.832%	$173.1407	$173.14	$173.15	$173.10
7 purchase totals =	$905.93		$1,008.4715	$1,008.48	$1,008.50	$1,008.30