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	$131.86	4.779%	$138.1616	$138.16	$138.15	$138.20
Purchase #2	$67.55	10.272%	$74.4887	$74.49	$74.50	$74.50
Purchase #3	$83.27	4.243%	$86.8031	$86.80	$86.80	$86.80
Purchase #4	$10.41	4.855%	$10.9154	$10.92	$10.90	$10.90
Purchase #5	$225.34	13.409%	$255.5558	$255.56	$255.55	$255.60
Purchase #6	$102.58	13.536%	$116.4652	$116.47	$116.45	$116.50
Purchase #7	$117.71	3.764%	$122.1406	$122.14	$122.15	$122.10
7 purchase totals =	$738.72		$804.5304	$804.54	$804.50	$804.60