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	$137.63	6.500%	$146.576	$146.58	$146.60	$146.60
Purchase #2	$144.51	5.365%	$152.263	$152.26	$152.25	$152.30
Purchase #3	$11.52	12.545%	$12.9652	$12.97	$12.95	$13.00
Purchase #4	$123.61	7.337%	$132.6793	$132.68	$132.70	$132.70
Purchase #5	$95.74	5.409%	$100.9186	$100.92	$100.90	$100.90
Purchase #6	$79.67	12.288%	$89.4598	$89.46	$89.45	$89.50
Purchase #7	$162.34	6.873%	$173.4976	$173.50	$173.50	$173.50
7 purchase totals =	$755.02		$808.3595	$808.37	$808.35	$808.50