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	$73.76	6.365%	$78.4548	$78.45	$78.45	$78.50
Purchase #2	$104.58	6.396%	$111.2689	$111.27	$111.25	$111.30
Purchase #3	$242.38	5.400%	$255.4685	$255.47	$255.45	$255.50
Purchase #4	$100.92	11.480%	$112.5056	$112.51	$112.50	$112.50
Purchase #5	$45.90	13.594%	$52.1396	$52.14	$52.15	$52.10
Purchase #6	$56.90	11.367%	$63.3678	$63.37	$63.35	$63.40
Purchase #7	$150.67	3.745%	$156.3126	$156.31	$156.30	$156.30
7 purchase totals =	$775.11		$829.5178	$829.52	$829.45	$829.60