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	$41.78	3.862%	$43.3935	$43.39	$43.40	$43.40
Purchase #2	$172.55	9.285%	$188.5713	$188.57	$188.55	$188.60
Purchase #3	$69.46	11.739%	$77.6139	$77.61	$77.60	$77.60
Purchase #4	$44.28	9.396%	$48.4405	$48.44	$48.45	$48.40
Purchase #5	$160.77	10.667%	$177.9193	$177.92	$177.90	$177.90
Purchase #6	$105.46	10.240%	$116.2591	$116.26	$116.25	$116.30
Purchase #7	$152.25	6.680%	$162.4203	$162.42	$162.40	$162.40
7 purchase totals =	$746.55		$814.6179	$814.61	$814.55	$814.60