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	$39.78	12.300%	$44.6729	$44.67	$44.65	$44.70
Purchase #2	$136.71	10.782%	$151.4501	$151.45	$151.45	$151.50
Purchase #3	$164.90	4.619%	$172.5167	$172.52	$172.50	$172.50
Purchase #4	$11.65	8.219%	$12.6075	$12.61	$12.60	$12.60
Purchase #5	$30.34	3.709%	$31.4653	$31.47	$31.45	$31.50
Purchase #6	$229.28	4.516%	$239.6343	$239.63	$239.65	$239.60
Purchase #7	$128.37	10.512%	$141.8643	$141.86	$141.85	$141.90
7 purchase totals =	$741.03		$794.2111	$794.21	$794.15	$794.30