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	$38.91	9.541%	$42.6224	$42.62	$42.60	$42.60
Purchase #2	$116.38	9.467%	$127.3977	$127.40	$127.40	$127.40
Purchase #3	$164.85	6.451%	$175.4845	$175.48	$175.50	$175.50
Purchase #4	$153.29	13.431%	$173.8784	$173.88	$173.90	$173.90
Purchase #5	$83.89	4.619%	$87.7649	$87.76	$87.75	$87.80
Purchase #6	$50.59	3.150%	$52.1836	$52.18	$52.20	$52.20
Purchase #7	$211.94	4.504%	$221.4858	$221.49	$221.50	$221.50
7 purchase totals =	$819.85		$880.8173	$880.81	$880.85	$880.90