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	$211.64	3.141%	$218.2876	$218.29	$218.30	$218.30
Purchase #2	$31.61	8.147%	$34.1853	$34.19	$34.20	$34.20
Purchase #3	$145.86	5.113%	$153.3178	$153.32	$153.30	$153.30
Purchase #4	$79.91	3.141%	$82.42	$82.42	$82.40	$82.40
Purchase #5	$232.55	13.566%	$264.0977	$264.10	$264.10	$264.10
Purchase #6	$160.55	4.103%	$167.1374	$167.14	$167.15	$167.10
Purchase #7	$54.32	13.397%	$61.5973	$61.60	$61.60	$61.60
7 purchase totals =	$916.44		$981.0431	$981.06	$981.05	$981.00