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	$77.89	12.126%	$87.3349	$87.33	$87.35	$87.30
Purchase #2	$78.41	11.275%	$87.2507	$87.25	$87.25	$87.30
Purchase #3	$11.88	8.539%	$12.8944	$12.89	$12.90	$12.90
Purchase #4	$78.62	9.104%	$85.7776	$85.78	$85.80	$85.80
Purchase #5	$223.46	8.150%	$241.672	$241.67	$241.65	$241.70
Purchase #6	$175.90	7.339%	$188.8093	$188.81	$188.80	$188.80
Purchase #7	$141.93	10.707%	$157.1264	$157.13	$157.15	$157.10
7 purchase totals =	$788.09		$860.8653	$860.86	$860.90	$860.90