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	$18.95	7.520%	$20.375	$20.38	$20.40	$20.40
Purchase #2	$49.58	9.118%	$54.1007	$54.10	$54.10	$54.10
Purchase #3	$21.96	5.109%	$23.0819	$23.08	$23.10	$23.10
Purchase #4	$140.96	10.394%	$155.6114	$155.61	$155.60	$155.60
Purchase #5	$17.65	5.105%	$18.551	$18.55	$18.55	$18.60
Purchase #6	$220.38	3.689%	$228.5098	$228.51	$228.50	$228.50
Purchase #7	$174.75	6.392%	$185.92	$185.92	$185.90	$185.90
7 purchase totals =	$644.23		$686.1498	$686.15	$686.15	$686.20