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	$104.47	4.366%	$109.0312	$109.03	$109.05	$109.00
Purchase #2	$130.65	9.618%	$143.2159	$143.22	$143.20	$143.20
Purchase #3	$249.93	3.527%	$258.745	$258.75	$258.75	$258.70
Purchase #4	$66.49	8.632%	$72.2294	$72.23	$72.25	$72.20
Purchase #5	$180.67	5.308%	$190.26	$190.26	$190.25	$190.30
Purchase #6	$223.60	3.727%	$231.9336	$231.93	$231.95	$231.90
Purchase #7	$22.71	10.687%	$25.137	$25.14	$25.15	$25.10
7 purchase totals =	$978.52		$1,030.5521	$1,030.56	$1,030.60	$1,030.40