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	$92.98	11.441%	$103.6178	$103.62	$103.60	$103.60
Purchase #2	$221.87	8.841%	$241.4855	$241.49	$241.50	$241.50
Purchase #3	$97.37	12.296%	$109.3426	$109.34	$109.35	$109.30
Purchase #4	$131.95	9.150%	$144.0234	$144.02	$144.00	$144.00
Purchase #5	$177.28	6.784%	$189.3067	$189.31	$189.30	$189.30
Purchase #6	$47.90	9.105%	$52.2613	$52.26	$52.25	$52.30
Purchase #7	$104.80	13.169%	$118.6011	$118.60	$118.60	$118.60
7 purchase totals =	$874.15		$958.6384	$958.64	$958.60	$958.60