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	$40.43	4.448%	$42.2283	$42.23	$42.25	$42.20
Purchase #2	$94.25	9.838%	$103.5223	$103.52	$103.50	$103.50
Purchase #3	$184.44	4.275%	$192.3248	$192.32	$192.30	$192.30
Purchase #4	$150.84	4.735%	$157.9823	$157.98	$158.00	$158.00
Purchase #5	$199.75	9.391%	$218.5085	$218.51	$218.50	$218.50
Purchase #6	$154.37	3.797%	$160.2314	$160.23	$160.25	$160.20
Purchase #7	$47.56	8.491%	$51.5983	$51.60	$51.60	$51.60
7 purchase totals =	$871.64		$926.3959	$926.39	$926.40	$926.30