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	$57.54	13.346%	$65.2193	$65.22	$65.20	$65.20
Purchase #2	$84.85	5.340%	$89.381	$89.38	$89.40	$89.40
Purchase #3	$138.31	8.789%	$150.4661	$150.47	$150.45	$150.50
Purchase #4	$54.73	7.128%	$58.6312	$58.63	$58.65	$58.60
Purchase #5	$187.75	5.630%	$198.3203	$198.32	$198.30	$198.30
Purchase #6	$37.36	4.266%	$38.9538	$38.95	$38.95	$39.00
Purchase #7	$241.86	10.810%	$268.0051	$268.01	$268.00	$268.00
7 purchase totals =	$802.40		$868.9768	$868.98	$868.95	$869.00