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	$54.27	5.111%	$57.0437	$57.04	$57.05	$57.00
Purchase #2	$222.62	5.472%	$234.8018	$234.80	$234.80	$234.80
Purchase #3	$100.81	10.383%	$111.2771	$111.28	$111.30	$111.30
Purchase #4	$18.92	10.817%	$20.9666	$20.97	$20.95	$21.00
Purchase #5	$139.95	7.405%	$150.3133	$150.31	$150.30	$150.30
Purchase #6	$105.28	3.778%	$109.2575	$109.26	$109.25	$109.30
Purchase #7	$120.97	4.586%	$126.5177	$126.52	$126.50	$126.50
7 purchase totals =	$762.82		$810.1777	$810.18	$810.15	$810.20