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	$131.30	11.542%	$146.4546	$146.45	$146.45	$146.50
Purchase #2	$113.30	4.457%	$118.3498	$118.35	$118.35	$118.30
Purchase #3	$91.38	13.852%	$104.038	$104.04	$104.05	$104.00
Purchase #4	$208.77	4.757%	$218.7012	$218.70	$218.70	$218.70
Purchase #5	$57.70	13.381%	$65.4208	$65.42	$65.40	$65.40
Purchase #6	$41.86	13.765%	$47.622	$47.62	$47.60	$47.60
Purchase #7	$223.91	6.484%	$238.4283	$238.43	$238.45	$238.40
7 purchase totals =	$868.22		$939.0147	$939.01	$939.00	$938.90