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	$46.69	9.578%	$51.162	$51.16	$51.15	$51.20
Purchase #2	$107.48	3.660%	$111.4138	$111.41	$111.40	$111.40
Purchase #3	$45.95	7.653%	$49.4666	$49.47	$49.45	$49.50
Purchase #4	$244.45	7.196%	$262.0406	$262.04	$262.05	$262.00
Purchase #5	$178.86	3.608%	$185.3133	$185.31	$185.30	$185.30
Purchase #6	$109.97	13.636%	$124.9655	$124.97	$124.95	$125.00
Purchase #7	$47.30	12.647%	$53.282	$53.28	$53.30	$53.30
7 purchase totals =	$780.70		$837.6438	$837.64	$837.60	$837.70