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	$59.91	10.847%	$66.4084	$66.41	$66.40	$66.40
Purchase #2	$227.55	6.149%	$241.542	$241.54	$241.55	$241.50
Purchase #3	$198.57	11.508%	$221.4214	$221.42	$221.40	$221.40
Purchase #4	$97.33	13.488%	$110.4579	$110.46	$110.45	$110.50
Purchase #5	$167.83	7.291%	$180.0665	$180.07	$180.05	$180.10
Purchase #6	$45.68	9.514%	$50.026	$50.03	$50.05	$50.00
Purchase #7	$137.68	9.146%	$150.2722	$150.27	$150.25	$150.30
7 purchase totals =	$934.55		$1,020.1944	$1,020.20	$1,020.15	$1,020.20