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	$236.42	13.756%	$268.9419	$268.94	$268.95	$268.90
Purchase #2	$210.66	13.189%	$238.4439	$238.44	$238.45	$238.40
Purchase #3	$50.26	5.343%	$52.9454	$52.95	$52.95	$52.90
Purchase #4	$77.86	7.104%	$83.3912	$83.39	$83.40	$83.40
Purchase #5	$33.97	4.144%	$35.3777	$35.38	$35.40	$35.40
Purchase #6	$90.38	12.147%	$101.3585	$101.36	$101.35	$101.40
Purchase #7	$90.30	10.332%	$99.6298	$99.63	$99.65	$99.60
7 purchase totals =	$789.85		$880.0884	$880.09	$880.15	$880.00