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	$10.50	12.800%	$11.844	$11.84	$11.85	$11.80
Purchase #2	$48.65	6.123%	$51.6288	$51.63	$51.65	$51.60
Purchase #3	$170.76	4.257%	$178.0293	$178.03	$178.05	$178.00
Purchase #4	$148.73	6.297%	$158.0955	$158.10	$158.10	$158.10
Purchase #5	$37.81	12.370%	$42.4871	$42.49	$42.50	$42.50
Purchase #6	$94.32	5.849%	$99.8368	$99.84	$99.85	$99.80
Purchase #7	$75.89	9.213%	$82.8817	$82.88	$82.90	$82.90
7 purchase totals =	$586.66		$624.8032	$624.81	$624.90	$624.70