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	$10.44	5.517%	$11.016	$11.02	$11.00	$11.00
Purchase #2	$19.30	13.111%	$21.8304	$21.83	$21.85	$21.80
Purchase #3	$154.46	6.744%	$164.8768	$164.88	$164.90	$164.90
Purchase #4	$11.83	6.626%	$12.6139	$12.61	$12.60	$12.60
Purchase #5	$237.46	9.265%	$259.4607	$259.46	$259.45	$259.50
Purchase #6	$135.77	5.731%	$143.551	$143.55	$143.55	$143.60
Purchase #7	$24.85	5.199%	$26.142	$26.14	$26.15	$26.10
7 purchase totals =	$594.11		$639.4908	$639.49	$639.50	$639.50