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	$249.78	6.390%	$265.7409	$265.74	$265.75	$265.70
Purchase #2	$237.37	7.336%	$254.7835	$254.78	$254.80	$254.80
Purchase #3	$208.52	8.194%	$225.6061	$225.61	$225.60	$225.60
Purchase #4	$48.82	13.279%	$55.3028	$55.30	$55.30	$55.30
Purchase #5	$85.47	5.510%	$90.1794	$90.18	$90.20	$90.20
Purchase #6	$241.26	5.634%	$254.8526	$254.85	$254.85	$254.90
Purchase #7	$134.80	6.460%	$143.5081	$143.51	$143.50	$143.50
7 purchase totals =	$1,206.02		$1,289.9734	$1,289.97	$1,290.00	$1,290.00