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	$157.97	7.376%	$169.6219	$169.62	$169.60	$169.60
Purchase #2	$177.51	7.122%	$190.1523	$190.15	$190.15	$190.20
Purchase #3	$90.45	12.677%	$101.9163	$101.92	$101.90	$101.90
Purchase #4	$106.48	12.220%	$119.4919	$119.49	$119.50	$119.50
Purchase #5	$51.95	6.601%	$55.3792	$55.38	$55.40	$55.40
Purchase #6	$240.38	9.618%	$263.4997	$263.50	$263.50	$263.50
Purchase #7	$85.52	5.386%	$90.1261	$90.13	$90.15	$90.10
7 purchase totals =	$910.26		$990.1874	$990.19	$990.20	$990.20