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	$77.49	7.514%	$83.3126	$83.31	$83.30	$83.30
Purchase #2	$219.86	13.353%	$249.2179	$249.22	$249.20	$249.20
Purchase #3	$36.55	7.483%	$39.285	$39.29	$39.30	$39.30
Purchase #4	$33.51	11.132%	$37.2403	$37.24	$37.25	$37.20
Purchase #5	$247.83	5.446%	$261.3268	$261.33	$261.35	$261.30
Purchase #6	$44.95	9.627%	$49.2773	$49.28	$49.30	$49.30
Purchase #7	$60.42	10.447%	$66.7321	$66.73	$66.75	$66.70
7 purchase totals =	$720.61		$786.3920	$786.40	$786.45	$786.30