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	$15.32	3.535%	$15.8616	$15.86	$15.85	$15.90
Purchase #2	$106.69	4.452%	$111.4398	$111.44	$111.45	$111.40
Purchase #3	$129.34	13.753%	$147.1281	$147.13	$147.15	$147.10
Purchase #4	$231.81	13.278%	$262.5897	$262.59	$262.60	$262.60
Purchase #5	$36.25	10.562%	$40.0787	$40.08	$40.10	$40.10
Purchase #6	$37.32	4.416%	$38.9681	$38.97	$38.95	$39.00
Purchase #7	$146.38	7.407%	$157.2224	$157.22	$157.20	$157.20
7 purchase totals =	$703.11		$773.2884	$773.29	$773.30	$773.30