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	$102.54	9.681%	$112.4669	$112.47	$112.45	$112.50
Purchase #2	$44.52	11.396%	$49.5935	$49.59	$49.60	$49.60
Purchase #3	$101.96	12.786%	$114.9966	$115.00	$115.00	$115.00
Purchase #4	$104.37	6.642%	$111.3023	$111.30	$111.30	$111.30
Purchase #5	$45.36	11.828%	$50.7252	$50.73	$50.75	$50.70
Purchase #6	$191.50	9.105%	$208.9361	$208.94	$208.95	$208.90
Purchase #7	$119.69	4.280%	$124.8127	$124.81	$124.80	$124.80
7 purchase totals =	$709.94		$772.8333	$772.84	$772.85	$772.80