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	$14.90	3.494%	$15.4206	$15.42	$15.40	$15.40
Purchase #2	$64.93	9.311%	$70.9756	$70.98	$71.00	$71.00
Purchase #3	$37.60	8.139%	$40.6603	$40.66	$40.65	$40.70
Purchase #4	$159.51	3.534%	$165.1471	$165.15	$165.15	$165.10
Purchase #5	$11.42	13.271%	$12.9355	$12.94	$12.95	$12.90
Purchase #6	$150.38	5.576%	$158.7652	$158.77	$158.75	$158.80
Purchase #7	$99.48	10.832%	$110.2557	$110.26	$110.25	$110.30
7 purchase totals =	$538.22		$574.1600	$574.18	$574.15	$574.20