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	$40.56	12.386%	$45.5838	$45.58	$45.60	$45.60
Purchase #2	$36.67	5.670%	$38.7492	$38.75	$38.75	$38.70
Purchase #3	$79.30	9.393%	$86.7486	$86.75	$86.75	$86.70
Purchase #4	$41.90	8.451%	$45.441	$45.44	$45.45	$45.40
Purchase #5	$168.60	10.870%	$186.9268	$186.93	$186.95	$186.90
Purchase #6	$80.38	12.477%	$90.409	$90.41	$90.40	$90.40
Purchase #7	$15.76	6.838%	$16.8377	$16.84	$16.85	$16.80
7 purchase totals =	$463.17		$510.6961	$510.70	$510.75	$510.50