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	$9.75	11.174%	$10.8395	$10.84	$10.85	$10.80
Purchase #2	$159.60	4.643%	$167.0102	$167.01	$167.00	$167.00
Purchase #3	$37.98	7.344%	$40.7693	$40.77	$40.75	$40.80
Purchase #4	$71.66	9.452%	$78.4333	$78.43	$78.45	$78.40
Purchase #5	$37.39	7.610%	$40.2354	$40.24	$40.25	$40.20
Purchase #6	$84.29	8.187%	$91.1908	$91.19	$91.20	$91.20
Purchase #7	$230.54	11.359%	$256.727	$256.73	$256.75	$256.70
7 purchase totals =	$631.21		$685.2055	$685.21	$685.25	$685.10