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	$190.64	12.143%	$213.7894	$213.79	$213.80	$213.80
Purchase #2	$176.71	5.231%	$185.9537	$185.95	$185.95	$186.00
Purchase #3	$108.32	13.712%	$123.1728	$123.17	$123.15	$123.20
Purchase #4	$24.47	11.624%	$27.3144	$27.31	$27.30	$27.30
Purchase #5	$25.68	5.150%	$27.0025	$27.00	$27.00	$27.00
Purchase #6	$22.98	11.731%	$25.6758	$25.68	$25.70	$25.70
Purchase #7	$52.66	13.223%	$59.6232	$59.62	$59.60	$59.60
7 purchase totals =	$601.46		$662.5318	$662.52	$662.50	$662.60