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	$207.50	13.187%	$234.863	$234.86	$234.85	$234.90
Purchase #2	$106.59	12.523%	$119.9383	$119.94	$119.95	$119.90
Purchase #3	$155.89	10.462%	$172.1992	$172.20	$172.20	$172.20
Purchase #4	$47.29	4.580%	$49.4559	$49.46	$49.45	$49.50
Purchase #5	$22.39	7.811%	$24.1389	$24.14	$24.15	$24.10
Purchase #6	$38.77	5.533%	$40.9151	$40.92	$40.90	$40.90
Purchase #7	$114.37	11.789%	$127.8531	$127.85	$127.85	$127.90
7 purchase totals =	$692.80		$769.3635	$769.37	$769.35	$769.40