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	$76.56	6.590%	$81.6053	$81.61	$81.60	$81.60
Purchase #2	$60.67	11.244%	$67.4917	$67.49	$67.50	$67.50
Purchase #3	$145.46	10.347%	$160.5107	$160.51	$160.50	$160.50
Purchase #4	$138.43	5.491%	$146.0312	$146.03	$146.05	$146.00
Purchase #5	$223.72	13.258%	$253.3808	$253.38	$253.40	$253.40
Purchase #6	$29.88	5.482%	$31.518	$31.52	$31.50	$31.50
Purchase #7	$55.28	7.296%	$59.3132	$59.31	$59.30	$59.30
7 purchase totals =	$730.00		$799.8509	$799.85	$799.85	$799.80