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	$35.37	9.389%	$38.6909	$38.69	$38.70	$38.70
Purchase #2	$92.83	13.371%	$105.2423	$105.24	$105.25	$105.20
Purchase #3	$128.88	8.303%	$139.5809	$139.58	$139.60	$139.60
Purchase #4	$119.45	10.828%	$132.384	$132.38	$132.40	$132.40
Purchase #5	$178.52	5.664%	$188.6314	$188.63	$188.65	$188.60
Purchase #6	$163.36	9.383%	$178.6881	$178.69	$178.70	$178.70
Purchase #7	$116.64	5.673%	$123.257	$123.26	$123.25	$123.30
7 purchase totals =	$835.05		$906.4746	$906.47	$906.55	$906.50