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	$80.26	11.543%	$89.5244	$89.52	$89.50	$89.50
Purchase #2	$225.72	9.206%	$246.4998	$246.50	$246.50	$246.50
Purchase #3	$89.40	7.800%	$96.3732	$96.37	$96.35	$96.40
Purchase #4	$34.51	13.351%	$39.1174	$39.12	$39.10	$39.10
Purchase #5	$186.96	9.766%	$205.2185	$205.22	$205.20	$205.20
Purchase #6	$145.77	10.214%	$160.6589	$160.66	$160.65	$160.70
Purchase #7	$40.38	6.745%	$43.1036	$43.10	$43.10	$43.10
7 purchase totals =	$803.00		$880.4958	$880.49	$880.40	$880.50