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	$136.38	4.217%	$142.1311	$142.13	$142.15	$142.10
Purchase #2	$116.66	9.591%	$127.8489	$127.85	$127.85	$127.80
Purchase #3	$99.74	5.217%	$104.9434	$104.94	$104.95	$104.90
Purchase #4	$47.61	3.701%	$49.372	$49.37	$49.35	$49.40
Purchase #5	$193.76	5.607%	$204.6241	$204.62	$204.60	$204.60
Purchase #6	$173.71	13.307%	$196.8256	$196.83	$196.85	$196.80
Purchase #7	$32.76	4.682%	$34.2938	$34.29	$34.30	$34.30
7 purchase totals =	$800.62		$860.0389	$860.03	$860.05	$859.90