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	$134.70	6.576%	$143.5579	$143.56	$143.55	$143.60
Purchase #2	$21.46	6.799%	$22.9191	$22.92	$22.90	$22.90
Purchase #3	$90.82	13.631%	$103.1997	$103.20	$103.20	$103.20
Purchase #4	$226.68	6.365%	$241.1082	$241.11	$241.10	$241.10
Purchase #5	$234.61	9.793%	$257.5854	$257.59	$257.60	$257.60
Purchase #6	$134.82	5.698%	$142.502	$142.50	$142.50	$142.50
Purchase #7	$71.80	9.841%	$78.8658	$78.87	$78.85	$78.90
7 purchase totals =	$914.89		$989.7381	$989.75	$989.70	$989.80