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	$12.46	10.130%	$13.7222	$13.72	$13.70	$13.70
Purchase #2	$158.33	3.589%	$164.0125	$164.01	$164.00	$164.00
Purchase #3	$37.99	7.496%	$40.8377	$40.84	$40.85	$40.80
Purchase #4	$179.45	11.797%	$200.6197	$200.62	$200.60	$200.60
Purchase #5	$105.94	7.777%	$114.179	$114.18	$114.20	$114.20
Purchase #6	$139.56	9.480%	$152.7903	$152.79	$152.80	$152.80
Purchase #7	$92.48	8.540%	$100.3778	$100.38	$100.40	$100.40
7 purchase totals =	$726.21		$786.5392	$786.54	$786.55	$786.50