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	$37.78	7.572%	$40.6407	$40.64	$40.65	$40.60
Purchase #2	$75.81	12.507%	$85.2916	$85.29	$85.30	$85.30
Purchase #3	$43.26	5.515%	$45.6458	$45.65	$45.65	$45.60
Purchase #4	$153.45	7.256%	$164.5843	$164.58	$164.60	$164.60
Purchase #5	$163.52	5.466%	$172.458	$172.46	$172.45	$172.50
Purchase #6	$129.57	6.773%	$138.3458	$138.35	$138.35	$138.30
Purchase #7	$208.30	10.591%	$230.3611	$230.36	$230.35	$230.40
7 purchase totals =	$811.69		$877.3273	$877.33	$877.35	$877.30