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	$14.34	10.561%	$15.8544	$15.85	$15.85	$15.90
Purchase #2	$32.59	6.721%	$34.7804	$34.78	$34.80	$34.80
Purchase #3	$174.72	7.330%	$187.527	$187.53	$187.55	$187.50
Purchase #4	$91.65	12.296%	$102.9193	$102.92	$102.90	$102.90
Purchase #5	$120.72	5.704%	$127.6059	$127.61	$127.60	$127.60
Purchase #6	$165.74	5.783%	$175.3247	$175.32	$175.30	$175.30
Purchase #7	$119.31	7.149%	$127.8395	$127.84	$127.85	$127.80
7 purchase totals =	$719.07		$771.8512	$771.85	$771.85	$771.80