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	$139.75	13.151%	$158.1285	$158.13	$158.15	$158.10
Purchase #2	$60.59	3.638%	$62.7943	$62.79	$62.80	$62.80
Purchase #3	$80.60	11.682%	$90.0157	$90.02	$90.00	$90.00
Purchase #4	$10.50	8.554%	$11.3982	$11.40	$11.40	$11.40
Purchase #5	$125.72	9.679%	$137.8884	$137.89	$137.90	$137.90
Purchase #6	$229.48	6.795%	$245.0732	$245.07	$245.05	$245.10
Purchase #7	$162.78	6.685%	$173.6618	$173.66	$173.65	$173.70
7 purchase totals =	$809.42		$878.9601	$878.96	$878.95	$879.00