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	$70.99	13.358%	$80.4728	$80.47	$80.45	$80.50
Purchase #2	$91.36	4.365%	$95.3479	$95.35	$95.35	$95.30
Purchase #3	$166.80	3.599%	$172.8031	$172.80	$172.80	$172.80
Purchase #4	$25.45	7.500%	$27.3588	$27.36	$27.35	$27.40
Purchase #5	$108.73	5.350%	$114.5471	$114.55	$114.55	$114.50
Purchase #6	$192.26	4.338%	$200.6002	$200.60	$200.60	$200.60
Purchase #7	$74.79	10.500%	$82.643	$82.64	$82.65	$82.60
7 purchase totals =	$730.38		$773.7729	$773.77	$773.75	$773.70