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	$130.82	9.440%	$143.1694	$143.17	$143.15	$143.20
Purchase #2	$242.67	13.371%	$275.1174	$275.12	$275.10	$275.10
Purchase #3	$106.45	4.335%	$111.0646	$111.06	$111.05	$111.10
Purchase #4	$21.46	13.574%	$24.373	$24.37	$24.35	$24.40
Purchase #5	$164.53	9.786%	$180.6309	$180.63	$180.65	$180.60
Purchase #6	$60.70	9.498%	$66.4653	$66.47	$66.45	$66.50
Purchase #7	$41.30	7.785%	$44.5152	$44.52	$44.50	$44.50
7 purchase totals =	$767.93		$845.3358	$845.34	$845.25	$845.40