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	$166.95	3.569%	$172.9084	$172.91	$172.90	$172.90
Purchase #2	$57.63	3.125%	$59.4309	$59.43	$59.45	$59.40
Purchase #3	$114.92	9.680%	$126.0443	$126.04	$126.05	$126.00
Purchase #4	$33.36	13.381%	$37.8239	$37.82	$37.80	$37.80
Purchase #5	$142.94	13.132%	$161.7109	$161.71	$161.70	$161.70
Purchase #6	$133.43	7.160%	$142.9836	$142.98	$143.00	$143.00
Purchase #7	$206.29	9.321%	$225.5183	$225.52	$225.50	$225.50
7 purchase totals =	$855.52		$926.4203	$926.41	$926.40	$926.30