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	$92.59	3.662%	$95.9806	$95.98	$96.00	$96.00
Purchase #2	$134.76	4.293%	$140.5452	$140.55	$140.55	$140.50
Purchase #3	$100.91	11.269%	$112.2815	$112.28	$112.30	$112.30
Purchase #4	$11.67	8.532%	$12.6657	$12.67	$12.65	$12.70
Purchase #5	$42.90	12.105%	$48.093	$48.09	$48.10	$48.10
Purchase #6	$71.96	11.694%	$80.375	$80.38	$80.40	$80.40
Purchase #7	$90.69	4.129%	$94.4346	$94.43	$94.45	$94.40
7 purchase totals =	$545.48		$584.3756	$584.38	$584.45	$584.40