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	$143.42	13.512%	$162.7989	$162.80	$162.80	$162.80
Purchase #2	$191.55	11.526%	$213.6281	$213.63	$213.65	$213.60
Purchase #3	$151.29	13.250%	$171.3359	$171.34	$171.35	$171.30
Purchase #4	$138.89	12.714%	$156.5485	$156.55	$156.55	$156.50
Purchase #5	$81.55	8.485%	$88.4695	$88.47	$88.45	$88.50
Purchase #6	$74.38	4.249%	$77.5404	$77.54	$77.55	$77.50
Purchase #7	$19.97	9.699%	$21.9069	$21.91	$21.90	$21.90
7 purchase totals =	$801.05		$892.2282	$892.24	$892.25	$892.10