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	$10.77	10.542%	$11.9054	$11.91	$11.90	$11.90
Purchase #2	$139.62	3.147%	$144.0138	$144.01	$144.00	$144.00
Purchase #3	$20.33	10.738%	$22.513	$22.51	$22.50	$22.50
Purchase #4	$164.91	13.316%	$186.8694	$186.87	$186.85	$186.90
Purchase #5	$82.85	9.155%	$90.4349	$90.43	$90.45	$90.40
Purchase #6	$48.92	11.563%	$54.5766	$54.58	$54.60	$54.60
Purchase #7	$163.72	10.279%	$180.5488	$180.55	$180.55	$180.50
7 purchase totals =	$631.12		$690.8619	$690.86	$690.85	$690.80