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	$69.78	12.640%	$78.6002	$78.60	$78.60	$78.60
Purchase #2	$241.67	11.231%	$268.812	$268.81	$268.80	$268.80
Purchase #3	$239.53	10.576%	$264.8627	$264.86	$264.85	$264.90
Purchase #4	$78.28	5.249%	$82.3889	$82.39	$82.40	$82.40
Purchase #5	$176.68	8.658%	$191.977	$191.98	$192.00	$192.00
Purchase #6	$147.42	10.129%	$162.3522	$162.35	$162.35	$162.40
Purchase #7	$48.66	7.857%	$52.4832	$52.48	$52.50	$52.50
7 purchase totals =	$1,002.02		$1,101.4762	$1,101.47	$1,101.50	$1,101.60