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	$35.72	4.149%	$37.202	$37.20	$37.20	$37.20
Purchase #2	$98.49	10.721%	$109.0491	$109.05	$109.05	$109.00
Purchase #3	$114.58	5.476%	$120.8544	$120.85	$120.85	$120.90
Purchase #4	$37.83	3.867%	$39.2929	$39.29	$39.30	$39.30
Purchase #5	$118.52	10.828%	$131.3533	$131.35	$131.35	$131.40
Purchase #6	$123.92	5.363%	$130.5658	$130.57	$130.55	$130.60
Purchase #7	$154.39	4.160%	$160.8126	$160.81	$160.80	$160.80
7 purchase totals =	$683.45		$729.1301	$729.12	$729.10	$729.20