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	$109.37	13.312%	$123.9293	$123.93	$123.95	$123.90
Purchase #2	$122.65	3.748%	$127.2469	$127.25	$127.25	$127.20
Purchase #3	$116.45	13.703%	$132.4071	$132.41	$132.40	$132.40
Purchase #4	$20.60	4.656%	$21.5591	$21.56	$21.55	$21.60
Purchase #5	$26.93	7.393%	$28.9209	$28.92	$28.90	$28.90
Purchase #6	$175.78	12.649%	$198.0144	$198.01	$198.00	$198.00
Purchase #7	$132.56	11.870%	$148.2949	$148.29	$148.30	$148.30
7 purchase totals =	$704.34		$780.3726	$780.37	$780.35	$780.30