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	$35.71	7.847%	$38.5122	$38.51	$38.50	$38.50
Purchase #2	$163.77	7.699%	$176.3787	$176.38	$176.40	$176.40
Purchase #3	$44.72	13.140%	$50.5962	$50.60	$50.60	$50.60
Purchase #4	$101.85	6.572%	$108.5436	$108.54	$108.55	$108.50
Purchase #5	$43.81	11.535%	$48.8635	$48.86	$48.85	$48.90
Purchase #6	$143.98	12.106%	$161.4102	$161.41	$161.40	$161.40
Purchase #7	$164.82	10.746%	$182.5316	$182.53	$182.55	$182.50
7 purchase totals =	$698.66		$766.8360	$766.83	$766.85	$766.80