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	$10.74	8.188%	$11.6194	$11.62	$11.60	$11.60
Purchase #2	$81.53	9.626%	$89.3781	$89.38	$89.40	$89.40
Purchase #3	$157.44	9.447%	$172.3134	$172.31	$172.30	$172.30
Purchase #4	$91.83	4.119%	$95.6125	$95.61	$95.60	$95.60
Purchase #5	$19.86	13.336%	$22.5085	$22.51	$22.50	$22.50
Purchase #6	$39.59	8.525%	$42.965	$42.97	$42.95	$43.00
Purchase #7	$214.64	5.734%	$226.9475	$226.95	$226.95	$226.90
7 purchase totals =	$615.63		$661.3444	$661.35	$661.30	$661.30