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	$50.41	13.526%	$57.2285	$57.23	$57.25	$57.20
Purchase #2	$163.70	5.539%	$172.7673	$172.77	$172.75	$172.80
Purchase #3	$150.50	11.472%	$167.7654	$167.77	$167.75	$167.80
Purchase #4	$238.36	13.766%	$271.1726	$271.17	$271.15	$271.20
Purchase #5	$67.51	5.869%	$71.4722	$71.47	$71.45	$71.50
Purchase #6	$138.86	8.698%	$150.938	$150.94	$150.95	$150.90
Purchase #7	$17.42	6.224%	$18.5042	$18.50	$18.50	$18.50
7 purchase totals =	$826.76		$909.8482	$909.85	$909.80	$909.90