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	$72.53	13.707%	$82.4717	$82.47	$82.45	$82.50
Purchase #2	$39.32	8.865%	$42.8057	$42.81	$42.80	$42.80
Purchase #3	$70.70	13.580%	$80.3011	$80.30	$80.30	$80.30
Purchase #4	$195.95	8.598%	$212.7978	$212.80	$212.80	$212.80
Purchase #5	$32.97	3.130%	$34.002	$34.00	$34.00	$34.00
Purchase #6	$44.39	5.259%	$46.7245	$46.72	$46.70	$46.70
Purchase #7	$54.54	8.698%	$59.2839	$59.28	$59.30	$59.30
7 purchase totals =	$510.40		$558.3867	$558.38	$558.35	$558.40