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	$11.41	10.737%	$12.6351	$12.64	$12.65	$12.60
Purchase #2	$92.45	12.389%	$103.9036	$103.90	$103.90	$103.90
Purchase #3	$40.97	6.647%	$43.6933	$43.69	$43.70	$43.70
Purchase #4	$101.93	11.250%	$113.3971	$113.40	$113.40	$113.40
Purchase #5	$184.69	10.787%	$204.6125	$204.61	$204.60	$204.60
Purchase #6	$57.44	3.329%	$59.3522	$59.35	$59.35	$59.40
Purchase #7	$129.65	9.274%	$141.6737	$141.67	$141.65	$141.70
7 purchase totals =	$618.54		$679.2675	$679.26	$679.25	$679.30