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	$138.82	6.219%	$147.4532	$147.45	$147.45	$147.50
Purchase #2	$115.87	3.289%	$119.681	$119.68	$119.70	$119.70
Purchase #3	$34.63	12.127%	$38.8296	$38.83	$38.85	$38.80
Purchase #4	$228.38	12.283%	$256.4319	$256.43	$256.45	$256.40
Purchase #5	$158.83	9.304%	$173.6075	$173.61	$173.60	$173.60
Purchase #6	$214.62	13.143%	$242.8275	$242.83	$242.85	$242.80
Purchase #7	$157.68	5.729%	$166.7135	$166.71	$166.70	$166.70
7 purchase totals =	$1,048.83		$1,145.5442	$1,145.54	$1,145.60	$1,145.50