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	$138.26	8.774%	$150.3909	$150.39	$150.40	$150.40
Purchase #2	$52.48	6.123%	$55.6934	$55.69	$55.70	$55.70
Purchase #3	$10.97	4.805%	$11.4971	$11.50	$11.50	$11.50
Purchase #4	$10.87	5.716%	$11.4913	$11.49	$11.50	$11.50
Purchase #5	$82.44	11.603%	$92.0055	$92.01	$92.00	$92.00
Purchase #6	$114.73	7.640%	$123.4954	$123.50	$123.50	$123.50
Purchase #7	$165.96	10.411%	$183.2381	$183.24	$183.25	$183.20
7 purchase totals =	$575.71		$627.8117	$627.82	$627.85	$627.80