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	$30.93	10.434%	$34.1572	$34.16	$34.15	$34.20
Purchase #2	$238.84	6.691%	$254.8208	$254.82	$254.80	$254.80
Purchase #3	$165.31	9.358%	$180.7797	$180.78	$180.80	$180.80
Purchase #4	$99.41	6.451%	$105.8229	$105.82	$105.80	$105.80
Purchase #5	$38.76	5.494%	$40.8895	$40.89	$40.90	$40.90
Purchase #6	$11.77	4.407%	$12.2887	$12.29	$12.30	$12.30
Purchase #7	$47.41	3.662%	$49.1462	$49.15	$49.15	$49.10
7 purchase totals =	$632.43		$677.9050	$677.91	$677.90	$677.90