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	$147.96	13.151%	$167.4182	$167.42	$167.40	$167.40
Purchase #2	$171.47	8.428%	$185.9215	$185.92	$185.90	$185.90
Purchase #3	$122.55	3.285%	$126.5758	$126.58	$126.60	$126.60
Purchase #4	$82.98	9.205%	$90.6183	$90.62	$90.60	$90.60
Purchase #5	$6.65	6.589%	$7.0882	$7.09	$7.10	$7.10
Purchase #6	$75.81	9.826%	$83.2591	$83.26	$83.25	$83.30
Purchase #7	$120.66	5.491%	$127.2854	$127.29	$127.30	$127.30
7 purchase totals =	$728.08		$788.1665	$788.18	$788.15	$788.20