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	$123.43	6.426%	$131.3616	$131.36	$131.35	$131.40
Purchase #2	$214.67	5.535%	$226.552	$226.55	$226.55	$226.60
Purchase #3	$131.30	10.472%	$145.0497	$145.05	$145.05	$145.00
Purchase #4	$229.60	9.718%	$251.9125	$251.91	$251.90	$251.90
Purchase #5	$216.80	3.722%	$224.8693	$224.87	$224.85	$224.90
Purchase #6	$11.39	10.686%	$12.6071	$12.61	$12.60	$12.60
Purchase #7	$25.89	6.532%	$27.5811	$27.58	$27.60	$27.60
7 purchase totals =	$953.08		$1,019.9333	$1,019.93	$1,019.90	$1,020.00