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	$245.38	5.549%	$258.9961	$259.00	$259.00	$259.00
Purchase #2	$111.61	7.666%	$120.166	$120.17	$120.15	$120.20
Purchase #3	$137.92	13.197%	$156.1213	$156.12	$156.10	$156.10
Purchase #4	$158.56	5.702%	$167.6011	$167.60	$167.60	$167.60
Purchase #5	$74.77	7.860%	$80.6469	$80.65	$80.65	$80.60
Purchase #6	$47.89	11.273%	$53.2886	$53.29	$53.30	$53.30
Purchase #7	$143.71	12.357%	$161.4682	$161.47	$161.45	$161.50
7 purchase totals =	$919.84		$998.2882	$998.30	$998.25	$998.30