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	$161.84	13.156%	$183.1317	$183.13	$183.15	$183.10
Purchase #2	$97.83	12.871%	$110.4217	$110.42	$110.40	$110.40
Purchase #3	$99.30	11.804%	$111.0214	$111.02	$111.00	$111.00
Purchase #4	$121.30	4.804%	$127.1273	$127.13	$127.15	$127.10
Purchase #5	$82.55	5.512%	$87.1002	$87.10	$87.10	$87.10
Purchase #6	$188.41	10.121%	$207.479	$207.48	$207.50	$207.50
Purchase #7	$129.72	10.286%	$143.063	$143.06	$143.05	$143.10
7 purchase totals =	$880.95		$969.3443	$969.34	$969.35	$969.30