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	$132.40	4.218%	$137.9846	$137.98	$138.00	$138.00
Purchase #2	$35.82	4.554%	$37.4512	$37.45	$37.45	$37.50
Purchase #3	$153.97	4.604%	$161.0588	$161.06	$161.05	$161.10
Purchase #4	$151.50	5.673%	$160.0946	$160.09	$160.10	$160.10
Purchase #5	$125.90	4.303%	$131.3175	$131.32	$131.30	$131.30
Purchase #6	$230.35	4.838%	$241.4943	$241.49	$241.50	$241.50
Purchase #7	$190.81	11.385%	$212.5337	$212.53	$212.55	$212.50
7 purchase totals =	$1,020.75		$1,081.9347	$1,081.92	$1,081.95	$1,082.00