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	$214.67	11.593%	$239.5567	$239.56	$239.55	$239.60
Purchase #2	$62.30	4.775%	$65.2748	$65.27	$65.25	$65.30
Purchase #3	$208.89	11.598%	$233.1171	$233.12	$233.10	$233.10
Purchase #4	$196.59	11.233%	$218.673	$218.67	$218.65	$218.70
Purchase #5	$133.62	7.409%	$143.5199	$143.52	$143.50	$143.50
Purchase #6	$30.83	3.340%	$31.8597	$31.86	$31.85	$31.90
Purchase #7	$65.45	3.304%	$67.6125	$67.61	$67.60	$67.60
7 purchase totals =	$912.35		$999.6137	$999.61	$999.50	$999.70