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	$131.63	10.504%	$145.4564	$145.46	$145.45	$145.50
Purchase #2	$226.28	13.500%	$256.8278	$256.83	$256.85	$256.80
Purchase #3	$142.64	12.790%	$160.8837	$160.88	$160.90	$160.90
Purchase #4	$196.80	9.208%	$214.9213	$214.92	$214.90	$214.90
Purchase #5	$119.40	5.816%	$126.3443	$126.34	$126.35	$126.30
Purchase #6	$154.83	10.191%	$170.6087	$170.61	$170.60	$170.60
Purchase #7	$40.54	13.185%	$45.8852	$45.89	$45.90	$45.90
7 purchase totals =	$1,012.12		$1,120.9274	$1,120.93	$1,120.95	$1,120.90