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	$245.96	10.575%	$271.9703	$271.97	$271.95	$272.00
Purchase #2	$221.51	4.672%	$231.8589	$231.86	$231.85	$231.90
Purchase #3	$87.52	12.854%	$98.7698	$98.77	$98.75	$98.80
Purchase #4	$103.69	5.307%	$109.1928	$109.19	$109.20	$109.20
Purchase #5	$21.90	10.186%	$24.1307	$24.13	$24.15	$24.10
Purchase #6	$142.59	5.552%	$150.5066	$150.51	$150.50	$150.50
Purchase #7	$19.71	5.809%	$20.855	$20.86	$20.85	$20.90
7 purchase totals =	$842.88		$907.2841	$907.29	$907.25	$907.40