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	$15.99	5.402%	$16.8538	$16.85	$16.85	$16.90
Purchase #2	$153.28	9.561%	$167.9351	$167.94	$167.95	$167.90
Purchase #3	$114.96	7.104%	$123.1268	$123.13	$123.15	$123.10
Purchase #4	$60.29	8.380%	$65.3423	$65.34	$65.35	$65.30
Purchase #5	$247.89	13.505%	$281.3675	$281.37	$281.35	$281.40
Purchase #6	$208.84	9.105%	$227.8549	$227.85	$227.85	$227.90
Purchase #7	$154.77	11.326%	$172.2993	$172.30	$172.30	$172.30
7 purchase totals =	$956.02		$1,054.7797	$1,054.78	$1,054.80	$1,054.80