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	$131.26	5.866%	$138.9597	$138.96	$138.95	$139.00
Purchase #2	$195.65	8.800%	$212.8672	$212.87	$212.85	$212.90
Purchase #3	$158.34	4.113%	$164.8525	$164.85	$164.85	$164.90
Purchase #4	$205.37	13.738%	$233.5837	$233.58	$233.60	$233.60
Purchase #5	$177.67	10.642%	$196.5776	$196.58	$196.60	$196.60
Purchase #6	$151.39	7.528%	$162.7866	$162.79	$162.80	$162.80
Purchase #7	$148.41	9.494%	$162.5	$162.50	$162.50	$162.50
7 purchase totals =	$1,168.09		$1,272.1273	$1,272.13	$1,272.15	$1,272.30