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	$101.64	6.576%	$108.3238	$108.32	$108.30	$108.30
Purchase #2	$154.83	3.448%	$160.1685	$160.17	$160.15	$160.20
Purchase #3	$142.40	9.867%	$156.4506	$156.45	$156.45	$156.50
Purchase #4	$93.25	13.212%	$105.5702	$105.57	$105.55	$105.60
Purchase #5	$65.89	6.575%	$70.2223	$70.22	$70.20	$70.20
Purchase #6	$63.77	5.138%	$67.0465	$67.05	$67.05	$67.00
Purchase #7	$67.29	10.611%	$74.4301	$74.43	$74.45	$74.40
7 purchase totals =	$689.07		$742.2120	$742.21	$742.15	$742.20