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	$76.38	5.293%	$80.4228	$80.42	$80.40	$80.40
Purchase #2	$147.61	11.706%	$164.8892	$164.89	$164.90	$164.90
Purchase #3	$138.32	9.707%	$151.7467	$151.75	$151.75	$151.70
Purchase #4	$141.50	6.804%	$151.1277	$151.13	$151.15	$151.10
Purchase #5	$155.26	12.348%	$174.4315	$174.43	$174.45	$174.40
Purchase #6	$154.70	9.455%	$169.3269	$169.33	$169.35	$169.30
Purchase #7	$59.71	13.213%	$67.5995	$67.60	$67.60	$67.60
7 purchase totals =	$873.48		$959.5443	$959.55	$959.60	$959.40