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	$20.58	11.709%	$22.9897	$22.99	$23.00	$23.00
Purchase #2	$196.61	10.155%	$216.5757	$216.58	$216.60	$216.60
Purchase #3	$233.49	7.452%	$250.8897	$250.89	$250.90	$250.90
Purchase #4	$233.53	6.816%	$249.4474	$249.45	$249.45	$249.40
Purchase #5	$13.90	12.341%	$15.6154	$15.62	$15.60	$15.60
Purchase #6	$160.64	7.196%	$172.1997	$172.20	$172.20	$172.20
Purchase #7	$204.52	4.499%	$213.7214	$213.72	$213.70	$213.70
7 purchase totals =	$1,063.27		$1,141.4390	$1,141.45	$1,141.45	$1,141.40