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	$136.34	9.412%	$149.1723	$149.17	$149.15	$149.20
Purchase #2	$51.28	12.710%	$57.7977	$57.80	$57.80	$57.80
Purchase #3	$118.33	11.182%	$131.5617	$131.56	$131.55	$131.60
Purchase #4	$24.40	8.479%	$26.4689	$26.47	$26.45	$26.50
Purchase #5	$79.96	13.737%	$90.9441	$90.94	$90.95	$90.90
Purchase #6	$28.39	13.744%	$32.2919	$32.29	$32.30	$32.30
Purchase #7	$238.43	13.675%	$271.0353	$271.04	$271.05	$271.00
7 purchase totals =	$677.13		$759.2719	$759.27	$759.25	$759.30