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	$198.89	11.694%	$222.1482	$222.15	$222.15	$222.10
Purchase #2	$108.51	13.618%	$123.2869	$123.29	$123.30	$123.30
Purchase #3	$42.43	6.649%	$45.2512	$45.25	$45.25	$45.30
Purchase #4	$132.81	7.248%	$142.4361	$142.44	$142.45	$142.40
Purchase #5	$185.80	3.599%	$192.4869	$192.49	$192.50	$192.50
Purchase #6	$44.65	8.587%	$48.4841	$48.48	$48.50	$48.50
Purchase #7	$5.77	6.847%	$6.1651	$6.17	$6.15	$6.20
7 purchase totals =	$718.86		$780.2585	$780.27	$780.30	$780.30