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	$156.86	10.818%	$173.8291	$173.83	$173.85	$173.80
Purchase #2	$34.89	13.251%	$39.5133	$39.51	$39.50	$39.50
Purchase #3	$90.58	13.451%	$102.7639	$102.76	$102.75	$102.80
Purchase #4	$28.97	13.516%	$32.8856	$32.89	$32.90	$32.90
Purchase #5	$100.73	10.794%	$111.6028	$111.60	$111.60	$111.60
Purchase #6	$156.37	13.692%	$177.7802	$177.78	$177.80	$177.80
Purchase #7	$181.83	3.782%	$188.7068	$188.71	$188.70	$188.70
7 purchase totals =	$750.23		$827.0817	$827.08	$827.10	$827.10