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	$106.75	5.377%	$112.4899	$112.49	$112.50	$112.50
Purchase #2	$38.42	3.770%	$39.8684	$39.87	$39.85	$39.90
Purchase #3	$129.30	5.767%	$136.7567	$136.76	$136.75	$136.80
Purchase #4	$58.99	5.679%	$62.34	$62.34	$62.35	$62.30
Purchase #5	$39.86	9.443%	$43.624	$43.62	$43.60	$43.60
Purchase #6	$51.92	5.468%	$54.759	$54.76	$54.75	$54.80
Purchase #7	$135.98	4.706%	$142.3792	$142.38	$142.40	$142.40
7 purchase totals =	$561.22		$592.2172	$592.22	$592.20	$592.30