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	$26.51	4.476%	$27.6966	$27.70	$27.70	$27.70
Purchase #2	$74.51	5.158%	$78.3532	$78.35	$78.35	$78.40
Purchase #3	$228.88	3.746%	$237.4538	$237.45	$237.45	$237.50
Purchase #4	$41.41	12.824%	$46.7204	$46.72	$46.70	$46.70
Purchase #5	$200.89	5.127%	$211.1896	$211.19	$211.20	$211.20
Purchase #6	$51.38	7.646%	$55.3085	$55.31	$55.30	$55.30
Purchase #7	$95.43	4.282%	$99.5163	$99.52	$99.50	$99.50
7 purchase totals =	$719.01		$756.2384	$756.24	$756.20	$756.30