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	$31.65	7.510%	$34.0269	$34.03	$34.05	$34.00
Purchase #2	$99.87	11.816%	$111.6706	$111.67	$111.65	$111.70
Purchase #3	$84.78	7.115%	$90.8121	$90.81	$90.80	$90.80
Purchase #4	$234.86	5.487%	$247.7468	$247.75	$247.75	$247.70
Purchase #5	$111.42	13.466%	$126.4238	$126.42	$126.40	$126.40
Purchase #6	$115.65	10.537%	$127.836	$127.84	$127.85	$127.80
Purchase #7	$134.63	11.680%	$150.3548	$150.35	$150.35	$150.40
7 purchase totals =	$812.86		$888.8710	$888.87	$888.85	$888.80