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	$80.56	12.434%	$90.5768	$90.58	$90.60	$90.60
Purchase #2	$167.76	3.554%	$173.7222	$173.72	$173.70	$173.70
Purchase #3	$178.31	6.463%	$189.8342	$189.83	$189.85	$189.80
Purchase #4	$48.66	13.524%	$55.2408	$55.24	$55.25	$55.20
Purchase #5	$160.89	9.248%	$175.7691	$175.77	$175.75	$175.80
Purchase #6	$21.58	4.172%	$22.4803	$22.48	$22.50	$22.50
Purchase #7	$67.83	3.313%	$70.0772	$70.08	$70.10	$70.10
7 purchase totals =	$725.59		$777.7006	$777.70	$777.75	$777.70