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	$37.34	10.416%	$41.2293	$41.23	$41.25	$41.20
Purchase #2	$152.60	9.827%	$167.596	$167.60	$167.60	$167.60
Purchase #3	$104.87	6.731%	$111.9288	$111.93	$111.95	$111.90
Purchase #4	$29.51	3.116%	$30.4295	$30.43	$30.45	$30.40
Purchase #5	$135.73	12.695%	$152.9609	$152.96	$152.95	$153.00
Purchase #6	$47.68	6.653%	$50.8522	$50.85	$50.85	$50.90
Purchase #7	$40.93	10.557%	$45.251	$45.25	$45.25	$45.30
7 purchase totals =	$548.66		$600.2477	$600.25	$600.30	$600.30