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	$132.60	5.114%	$139.3812	$139.38	$139.40	$139.40
Purchase #2	$111.62	9.632%	$122.3712	$122.37	$122.35	$122.40
Purchase #3	$209.85	13.601%	$238.3917	$238.39	$238.40	$238.40
Purchase #4	$160.39	5.316%	$168.9163	$168.92	$168.90	$168.90
Purchase #5	$29.88	8.768%	$32.4999	$32.50	$32.50	$32.50
Purchase #6	$236.90	11.293%	$263.6531	$263.65	$263.65	$263.70
Purchase #7	$96.91	9.167%	$105.7937	$105.79	$105.80	$105.80
7 purchase totals =	$978.15		$1,071.0071	$1,071.00	$1,071.00	$1,071.10