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	$20.67	12.771%	$23.3098	$23.31	$23.30	$23.30
Purchase #2	$85.94	5.584%	$90.7389	$90.74	$90.75	$90.70
Purchase #3	$78.45	9.343%	$85.7796	$85.78	$85.80	$85.80
Purchase #4	$43.61	9.142%	$47.5968	$47.60	$47.60	$47.60
Purchase #5	$10.69	13.458%	$12.1287	$12.13	$12.15	$12.10
Purchase #6	$228.85	10.745%	$253.4399	$253.44	$253.45	$253.40
Purchase #7	$38.28	10.200%	$42.1846	$42.18	$42.20	$42.20
7 purchase totals =	$506.49		$555.1783	$555.18	$555.25	$555.10