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	$216.71	10.874%	$240.275	$240.28	$240.30	$240.30
Purchase #2	$78.94	10.336%	$87.0992	$87.10	$87.10	$87.10
Purchase #3	$34.85	8.758%	$37.9022	$37.90	$37.90	$37.90
Purchase #4	$233.69	6.642%	$249.2117	$249.21	$249.20	$249.20
Purchase #5	$18.52	11.113%	$20.5781	$20.58	$20.60	$20.60
Purchase #6	$111.26	3.456%	$115.1051	$115.11	$115.10	$115.10
Purchase #7	$35.77	13.640%	$40.649	$40.65	$40.65	$40.60
7 purchase totals =	$729.74		$790.8203	$790.83	$790.85	$790.80