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	$180.51	6.664%	$192.5392	$192.54	$192.55	$192.50
Purchase #2	$147.63	5.605%	$155.9047	$155.90	$155.90	$155.90
Purchase #3	$142.47	6.339%	$151.5012	$151.50	$151.50	$151.50
Purchase #4	$145.39	7.603%	$156.444	$156.44	$156.45	$156.40
Purchase #5	$126.84	3.666%	$131.49	$131.49	$131.50	$131.50
Purchase #6	$106.77	9.384%	$116.7893	$116.79	$116.80	$116.80
Purchase #7	$49.98	8.686%	$54.3213	$54.32	$54.30	$54.30
7 purchase totals =	$899.59		$958.9897	$958.98	$959.00	$958.90