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	$85.30	4.496%	$89.1351	$89.14	$89.15	$89.10
Purchase #2	$40.48	12.548%	$45.5594	$45.56	$45.55	$45.60
Purchase #3	$230.34	8.835%	$250.6905	$250.69	$250.70	$250.70
Purchase #4	$123.79	5.520%	$130.6232	$130.62	$130.60	$130.60
Purchase #5	$183.93	6.199%	$195.3318	$195.33	$195.35	$195.30
Purchase #6	$231.51	11.364%	$257.8188	$257.82	$257.80	$257.80
Purchase #7	$231.81	4.293%	$241.7616	$241.76	$241.75	$241.80
7 purchase totals =	$1,127.16		$1,210.9204	$1,210.92	$1,210.90	$1,210.90