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	$34.57	7.665%	$37.2198	$37.22	$37.20	$37.20
Purchase #2	$100.61	10.686%	$111.3612	$111.36	$111.35	$111.40
Purchase #3	$138.59	5.293%	$145.9256	$145.93	$145.95	$145.90
Purchase #4	$77.41	7.235%	$83.0106	$83.01	$83.00	$83.00
Purchase #5	$68.92	7.780%	$74.282	$74.28	$74.30	$74.30
Purchase #6	$41.34	12.802%	$46.6323	$46.63	$46.65	$46.60
Purchase #7	$48.30	4.153%	$50.3059	$50.31	$50.30	$50.30
7 purchase totals =	$509.74		$548.7374	$548.74	$548.75	$548.70