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	$29.67	3.153%	$30.6055	$30.61	$30.60	$30.60
Purchase #2	$74.44	8.583%	$80.8292	$80.83	$80.85	$80.80
Purchase #3	$130.65	7.548%	$140.5115	$140.51	$140.50	$140.50
Purchase #4	$91.64	9.708%	$100.5364	$100.54	$100.55	$100.50
Purchase #5	$59.30	9.784%	$65.1019	$65.10	$65.10	$65.10
Purchase #6	$10.94	10.231%	$12.0593	$12.06	$12.05	$12.10
Purchase #7	$179.49	3.378%	$185.5532	$185.55	$185.55	$185.60
7 purchase totals =	$576.13		$615.1970	$615.20	$615.20	$615.20