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	$6.48	8.202%	$7.0115	$7.01	$7.00	$7.00
Purchase #2	$87.78	9.699%	$96.2938	$96.29	$96.30	$96.30
Purchase #3	$31.83	7.697%	$34.28	$34.28	$34.30	$34.30
Purchase #4	$203.27	9.467%	$222.5136	$222.51	$222.50	$222.50
Purchase #5	$91.76	10.522%	$101.415	$101.42	$101.40	$101.40
Purchase #6	$80.40	12.183%	$90.1951	$90.20	$90.20	$90.20
Purchase #7	$50.26	4.680%	$52.6122	$52.61	$52.60	$52.60
7 purchase totals =	$551.78		$604.3212	$604.32	$604.30	$604.30