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	$5.68	13.192%	$6.4293	$6.43	$6.45	$6.40
Purchase #2	$205.57	11.363%	$228.9289	$228.93	$228.95	$228.90
Purchase #3	$103.66	8.280%	$112.243	$112.24	$112.25	$112.20
Purchase #4	$168.26	11.776%	$188.0743	$188.07	$188.05	$188.10
Purchase #5	$78.90	8.372%	$85.5055	$85.51	$85.50	$85.50
Purchase #6	$109.28	10.169%	$120.3927	$120.39	$120.40	$120.40
Purchase #7	$121.62	4.432%	$127.0102	$127.01	$127.00	$127.00
7 purchase totals =	$792.97		$868.5839	$868.58	$868.60	$868.50