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	$33.27	13.549%	$37.7778	$37.78	$37.80	$37.80
Purchase #2	$144.38	12.696%	$162.7105	$162.71	$162.70	$162.70
Purchase #3	$238.29	11.194%	$264.9642	$264.96	$264.95	$265.00
Purchase #4	$150.79	5.185%	$158.6085	$158.61	$158.60	$158.60
Purchase #5	$248.35	10.550%	$274.5509	$274.55	$274.55	$274.60
Purchase #6	$78.92	11.287%	$87.8277	$87.83	$87.85	$87.80
Purchase #7	$211.43	3.503%	$218.8364	$218.84	$218.85	$218.80
7 purchase totals =	$1,105.43		$1,205.2760	$1,205.28	$1,205.30	$1,205.30