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	$26.47	4.256%	$27.5966	$27.60	$27.60	$27.60
Purchase #2	$142.98	10.389%	$157.8342	$157.83	$157.85	$157.80
Purchase #3	$104.51	5.169%	$109.9121	$109.91	$109.90	$109.90
Purchase #4	$125.63	6.484%	$133.7758	$133.78	$133.80	$133.80
Purchase #5	$197.25	10.817%	$218.5865	$218.59	$218.60	$218.60
Purchase #6	$48.97	11.488%	$54.5957	$54.60	$54.60	$54.60
Purchase #7	$71.79	8.652%	$78.0013	$78.00	$78.00	$78.00
7 purchase totals =	$717.60		$780.3022	$780.31	$780.35	$780.30