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	$111.51	7.316%	$119.6681	$119.67	$119.65	$119.70
Purchase #2	$115.86	9.195%	$126.5133	$126.51	$126.50	$126.50
Purchase #3	$70.58	11.277%	$78.5393	$78.54	$78.55	$78.50
Purchase #4	$20.49	3.874%	$21.2838	$21.28	$21.30	$21.30
Purchase #5	$67.99	6.198%	$72.204	$72.20	$72.20	$72.20
Purchase #6	$49.66	8.356%	$53.8096	$53.81	$53.80	$53.80
Purchase #7	$111.29	8.582%	$120.8409	$120.84	$120.85	$120.80
7 purchase totals =	$547.38		$592.8590	$592.85	$592.85	$592.80