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	$94.77	5.200%	$99.698	$99.70	$99.70	$99.70
Purchase #2	$44.25	9.789%	$48.5816	$48.58	$48.60	$48.60
Purchase #3	$160.99	10.693%	$178.2047	$178.20	$178.20	$178.20
Purchase #4	$79.77	12.796%	$89.9774	$89.98	$90.00	$90.00
Purchase #5	$132.57	9.278%	$144.8698	$144.87	$144.85	$144.90
Purchase #6	$85.86	4.134%	$89.4095	$89.41	$89.40	$89.40
Purchase #7	$122.40	8.484%	$132.7844	$132.78	$132.80	$132.80
7 purchase totals =	$720.61		$783.5254	$783.52	$783.55	$783.60