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	$178.92	6.640%	$190.8003	$190.80	$190.80	$190.80
Purchase #2	$31.30	3.786%	$32.485	$32.49	$32.50	$32.50
Purchase #3	$19.42	4.470%	$20.2881	$20.29	$20.30	$20.30
Purchase #4	$237.96	10.666%	$263.3408	$263.34	$263.35	$263.30
Purchase #5	$81.25	6.162%	$86.2566	$86.26	$86.25	$86.30
Purchase #6	$78.38	8.239%	$84.8377	$84.84	$84.85	$84.80
Purchase #7	$95.59	6.850%	$102.1379	$102.14	$102.15	$102.10
7 purchase totals =	$722.82		$780.1464	$780.16	$780.20	$780.10