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	$126.82	7.473%	$136.2973	$136.30	$136.30	$136.30
Purchase #2	$116.66	9.570%	$127.8244	$127.82	$127.80	$127.80
Purchase #3	$211.66	6.594%	$225.6169	$225.62	$225.60	$225.60
Purchase #4	$219.73	4.485%	$229.5849	$229.58	$229.60	$229.60
Purchase #5	$235.89	7.510%	$253.6053	$253.61	$253.60	$253.60
Purchase #6	$26.83	7.344%	$28.8004	$28.80	$28.80	$28.80
Purchase #7	$108.51	13.363%	$123.0102	$123.01	$123.00	$123.00
7 purchase totals =	$1,046.10		$1,124.7394	$1,124.74	$1,124.70	$1,124.70