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	$243.25	13.150%	$275.2374	$275.24	$275.25	$275.20
Purchase #2	$44.45	9.589%	$48.7123	$48.71	$48.70	$48.70
Purchase #3	$35.27	5.691%	$37.2772	$37.28	$37.30	$37.30
Purchase #4	$75.42	10.681%	$83.4756	$83.48	$83.50	$83.50
Purchase #5	$122.27	11.444%	$136.2626	$136.26	$136.25	$136.30
Purchase #6	$241.58	12.626%	$272.0819	$272.08	$272.10	$272.10
Purchase #7	$222.90	3.130%	$229.8768	$229.88	$229.90	$229.90
7 purchase totals =	$985.14		$1,082.9238	$1,082.93	$1,083.00	$1,083.00