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	$71.96	11.409%	$80.1699	$80.17	$80.15	$80.20
Purchase #2	$13.43	7.561%	$14.4454	$14.45	$14.45	$14.40
Purchase #3	$83.43	4.793%	$87.4288	$87.43	$87.45	$87.40
Purchase #4	$121.40	12.705%	$136.8239	$136.82	$136.80	$136.80
Purchase #5	$83.85	7.514%	$90.1505	$90.15	$90.15	$90.20
Purchase #6	$240.50	6.488%	$256.1036	$256.10	$256.10	$256.10
Purchase #7	$9.47	10.165%	$10.4326	$10.43	$10.45	$10.40
7 purchase totals =	$624.04		$675.5547	$675.55	$675.55	$675.50