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	$20.37	9.815%	$22.3693	$22.37	$22.35	$22.40
Purchase #2	$46.92	13.492%	$53.2504	$53.25	$53.25	$53.30
Purchase #3	$181.61	4.861%	$190.4381	$190.44	$190.45	$190.40
Purchase #4	$152.42	11.696%	$170.247	$170.25	$170.25	$170.20
Purchase #5	$65.88	10.200%	$72.5998	$72.60	$72.60	$72.60
Purchase #6	$39.66	13.528%	$45.0252	$45.03	$45.05	$45.00
Purchase #7	$224.50	4.323%	$234.2051	$234.21	$234.20	$234.20
7 purchase totals =	$731.36		$788.1349	$788.15	$788.15	$788.10