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	$32.85	3.836%	$34.1101	$34.11	$34.10	$34.10
Purchase #2	$37.62	4.337%	$39.2516	$39.25	$39.25	$39.30
Purchase #3	$95.32	3.309%	$98.4741	$98.47	$98.45	$98.50
Purchase #4	$57.90	11.394%	$64.4971	$64.50	$64.50	$64.50
Purchase #5	$21.92	5.510%	$23.1278	$23.13	$23.15	$23.10
Purchase #6	$104.90	13.262%	$118.8118	$118.81	$118.80	$118.80
Purchase #7	$55.91	9.423%	$61.1784	$61.18	$61.20	$61.20
7 purchase totals =	$406.42		$439.4509	$439.45	$439.45	$439.50