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	$60.61	11.825%	$67.7771	$67.78	$67.80	$67.80
Purchase #2	$28.88	6.689%	$30.8118	$30.81	$30.80	$30.80
Purchase #3	$145.93	8.863%	$158.8638	$158.86	$158.85	$158.90
Purchase #4	$79.44	5.171%	$83.5478	$83.55	$83.55	$83.50
Purchase #5	$73.60	7.222%	$78.9154	$78.92	$78.90	$78.90
Purchase #6	$60.80	8.836%	$66.1723	$66.17	$66.15	$66.20
Purchase #7	$73.51	13.240%	$83.2427	$83.24	$83.25	$83.20
7 purchase totals =	$522.77		$569.3309	$569.33	$569.30	$569.30