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	$222.38	13.111%	$251.5362	$251.54	$251.55	$251.50
Purchase #2	$40.66	8.652%	$44.1779	$44.18	$44.20	$44.20
Purchase #3	$72.72	7.624%	$78.2642	$78.26	$78.25	$78.30
Purchase #4	$67.45	10.679%	$74.653	$74.65	$74.65	$74.70
Purchase #5	$101.78	10.498%	$112.4649	$112.46	$112.45	$112.50
Purchase #6	$53.96	5.289%	$56.8139	$56.81	$56.80	$56.80
Purchase #7	$49.85	6.271%	$52.9761	$52.98	$53.00	$53.00
7 purchase totals =	$608.80		$670.8862	$670.88	$670.90	$671.00