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	$22.58	10.345%	$24.9159	$24.92	$24.90	$24.90
Purchase #2	$40.78	8.735%	$44.3421	$44.34	$44.35	$44.30
Purchase #3	$57.47	5.803%	$60.805	$60.81	$60.80	$60.80
Purchase #4	$116.62	11.790%	$130.3695	$130.37	$130.35	$130.40
Purchase #5	$160.86	12.862%	$181.5498	$181.55	$181.55	$181.50
Purchase #6	$137.54	4.784%	$144.1199	$144.12	$144.10	$144.10
Purchase #7	$37.97	9.113%	$41.4302	$41.43	$41.45	$41.40
7 purchase totals =	$573.82		$627.5324	$627.54	$627.50	$627.40