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	$99.86	6.622%	$106.4727	$106.47	$106.45	$106.50
Purchase #2	$46.70	13.592%	$53.0475	$53.05	$53.05	$53.00
Purchase #3	$46.99	5.809%	$49.7196	$49.72	$49.70	$49.70
Purchase #4	$101.79	9.337%	$111.2941	$111.29	$111.30	$111.30
Purchase #5	$92.30	11.331%	$102.7585	$102.76	$102.75	$102.80
Purchase #6	$56.99	8.284%	$61.7111	$61.71	$61.70	$61.70
Purchase #7	$85.71	5.310%	$90.2612	$90.26	$90.25	$90.30
7 purchase totals =	$530.34		$575.2647	$575.26	$575.20	$575.30