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	$206.79	11.794%	$231.1788	$231.18	$231.20	$231.20
Purchase #2	$214.54	7.341%	$230.2894	$230.29	$230.30	$230.30
Purchase #3	$249.90	12.763%	$281.7947	$281.79	$281.80	$281.80
Purchase #4	$179.64	9.189%	$196.1471	$196.15	$196.15	$196.10
Purchase #5	$167.72	13.510%	$190.379	$190.38	$190.40	$190.40
Purchase #6	$23.43	10.441%	$25.8763	$25.88	$25.90	$25.90
Purchase #7	$135.59	7.312%	$145.5043	$145.50	$145.50	$145.50
7 purchase totals =	$1,177.61		$1,301.1696	$1,301.17	$1,301.25	$1,301.20