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	$100.45	5.137%	$105.6101	$105.61	$105.60	$105.60
Purchase #2	$137.53	10.171%	$151.5182	$151.52	$151.50	$151.50
Purchase #3	$132.87	7.767%	$143.19	$143.19	$143.20	$143.20
Purchase #4	$106.45	6.480%	$113.348	$113.35	$113.35	$113.30
Purchase #5	$37.73	5.669%	$39.8689	$39.87	$39.85	$39.90
Purchase #6	$86.51	5.783%	$91.5129	$91.51	$91.50	$91.50
Purchase #7	$91.58	4.178%	$95.4062	$95.41	$95.40	$95.40
7 purchase totals =	$693.12		$740.4543	$740.46	$740.40	$740.40