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	$35.68	11.149%	$39.658	$39.66	$39.65	$39.70
Purchase #2	$173.99	6.197%	$184.7722	$184.77	$184.75	$184.80
Purchase #3	$58.62	5.272%	$61.7104	$61.71	$61.70	$61.70
Purchase #4	$228.93	3.740%	$237.492	$237.49	$237.50	$237.50
Purchase #5	$132.76	11.670%	$148.2531	$148.25	$148.25	$148.30
Purchase #6	$82.89	9.106%	$90.438	$90.44	$90.45	$90.40
Purchase #7	$53.38	11.509%	$59.5235	$59.52	$59.50	$59.50
7 purchase totals =	$766.25		$821.8472	$821.84	$821.80	$821.90