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	$74.36	12.398%	$83.5792	$83.58	$83.60	$83.60
Purchase #2	$156.40	10.197%	$172.3481	$172.35	$172.35	$172.30
Purchase #3	$29.86	8.602%	$32.4286	$32.43	$32.45	$32.40
Purchase #4	$66.55	9.604%	$72.9415	$72.94	$72.95	$72.90
Purchase #5	$31.76	4.551%	$33.2054	$33.21	$33.20	$33.20
Purchase #6	$184.25	4.245%	$192.0714	$192.07	$192.05	$192.10
Purchase #7	$37.35	10.116%	$41.1283	$41.13	$41.15	$41.10
7 purchase totals =	$580.53		$627.7025	$627.71	$627.75	$627.60