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	$132.82	4.682%	$139.0386	$139.04	$139.05	$139.00
Purchase #2	$167.47	6.836%	$178.9182	$178.92	$178.90	$178.90
Purchase #3	$180.41	10.531%	$199.409	$199.41	$199.40	$199.40
Purchase #4	$135.52	13.191%	$153.3964	$153.40	$153.40	$153.40
Purchase #5	$117.57	11.711%	$131.3386	$131.34	$131.35	$131.30
Purchase #6	$206.49	13.286%	$233.9243	$233.92	$233.90	$233.90
Purchase #7	$12.75	6.358%	$13.5606	$13.56	$13.55	$13.60
7 purchase totals =	$953.03		$1,049.5857	$1,049.59	$1,049.55	$1,049.50