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	$100.73	12.696%	$113.5187	$113.52	$113.50	$113.50
Purchase #2	$62.37	11.688%	$69.6598	$69.66	$69.65	$69.70
Purchase #3	$129.72	3.153%	$133.8101	$133.81	$133.80	$133.80
Purchase #4	$45.30	5.627%	$47.849	$47.85	$47.85	$47.80
Purchase #5	$81.60	4.325%	$85.1292	$85.13	$85.15	$85.10
Purchase #6	$103.81	9.222%	$113.3834	$113.38	$113.40	$113.40
Purchase #7	$36.62	4.511%	$38.2719	$38.27	$38.25	$38.30
7 purchase totals =	$560.15		$601.6221	$601.62	$601.60	$601.60