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	$157.79	10.617%	$174.5426	$174.54	$174.55	$174.50
Purchase #2	$51.99	6.284%	$55.2571	$55.26	$55.25	$55.30
Purchase #3	$112.38	8.577%	$122.0188	$122.02	$122.00	$122.00
Purchase #4	$200.59	10.820%	$222.2938	$222.29	$222.30	$222.30
Purchase #5	$191.96	13.412%	$217.7057	$217.71	$217.70	$217.70
Purchase #6	$104.43	6.868%	$111.6023	$111.60	$111.60	$111.60
Purchase #7	$80.62	12.698%	$90.8571	$90.86	$90.85	$90.90
7 purchase totals =	$899.76		$994.2774	$994.28	$994.25	$994.30