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	$36.95	6.767%	$39.4504	$39.45	$39.45	$39.50
Purchase #2	$175.82	4.556%	$183.8304	$183.83	$183.85	$183.80
Purchase #3	$193.94	13.573%	$220.2635	$220.26	$220.25	$220.30
Purchase #4	$136.93	3.644%	$141.9197	$141.92	$141.90	$141.90
Purchase #5	$132.28	5.856%	$140.0263	$140.03	$140.05	$140.00
Purchase #6	$120.71	5.352%	$127.1704	$127.17	$127.15	$127.20
Purchase #7	$198.49	5.202%	$208.8154	$208.82	$208.80	$208.80
7 purchase totals =	$995.12		$1,061.4761	$1,061.48	$1,061.45	$1,061.50