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	$94.58	6.702%	$100.9188	$100.92	$100.90	$100.90
Purchase #2	$115.49	3.121%	$119.0944	$119.09	$119.10	$119.10
Purchase #3	$89.58	4.250%	$93.3872	$93.39	$93.40	$93.40
Purchase #4	$206.36	5.230%	$217.1526	$217.15	$217.15	$217.20
Purchase #5	$210.32	10.128%	$231.6212	$231.62	$231.60	$231.60
Purchase #6	$52.67	12.834%	$59.4297	$59.43	$59.45	$59.40
Purchase #7	$173.28	9.658%	$190.0154	$190.02	$190.00	$190.00
7 purchase totals =	$942.28		$1,011.6193	$1,011.62	$1,011.60	$1,011.60