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	$87.74	3.561%	$90.8644	$90.86	$90.85	$90.90
Purchase #2	$146.67	10.409%	$161.9369	$161.94	$161.95	$161.90
Purchase #3	$64.40	13.261%	$72.9401	$72.94	$72.95	$72.90
Purchase #4	$149.59	10.520%	$165.3269	$165.33	$165.35	$165.30
Purchase #5	$22.92	7.492%	$24.6372	$24.64	$24.65	$24.60
Purchase #6	$38.95	5.464%	$41.0782	$41.08	$41.10	$41.10
Purchase #7	$47.54	5.811%	$50.3025	$50.30	$50.30	$50.30
7 purchase totals =	$557.81		$607.0862	$607.09	$607.15	$607.00