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	$16.64	11.722%	$18.5905	$18.59	$18.60	$18.60
Purchase #2	$53.79	10.244%	$59.3002	$59.30	$59.30	$59.30
Purchase #3	$57.27	7.120%	$61.3476	$61.35	$61.35	$61.30
Purchase #4	$174.99	9.768%	$192.083	$192.08	$192.10	$192.10
Purchase #5	$114.30	11.224%	$127.129	$127.13	$127.15	$127.10
Purchase #6	$46.95	9.707%	$51.5074	$51.51	$51.50	$51.50
Purchase #7	$26.75	5.308%	$28.1699	$28.17	$28.15	$28.20
7 purchase totals =	$490.69		$538.1276	$538.13	$538.15	$538.10