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	$106.64	4.854%	$111.8163	$111.82	$111.80	$111.80
Purchase #2	$18.73	6.607%	$19.9675	$19.97	$19.95	$20.00
Purchase #3	$29.95	11.551%	$33.4095	$33.41	$33.40	$33.40
Purchase #4	$183.64	7.180%	$196.8254	$196.83	$196.85	$196.80
Purchase #5	$168.60	4.708%	$176.5377	$176.54	$176.55	$176.50
Purchase #6	$82.78	12.581%	$93.1946	$93.19	$93.20	$93.20
Purchase #7	$226.27	13.724%	$257.3233	$257.32	$257.30	$257.30
7 purchase totals =	$816.61		$889.0743	$889.08	$889.05	$889.00