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	$122.45	13.833%	$139.3885	$139.39	$139.40	$139.40
Purchase #2	$40.74	12.743%	$45.9315	$45.93	$45.95	$45.90
Purchase #3	$215.68	13.459%	$244.7084	$244.71	$244.70	$244.70
Purchase #4	$199.28	9.605%	$218.4208	$218.42	$218.40	$218.40
Purchase #5	$211.38	5.212%	$222.3971	$222.40	$222.40	$222.40
Purchase #6	$19.33	10.794%	$21.4165	$21.42	$21.40	$21.40
Purchase #7	$64.41	12.711%	$72.5972	$72.60	$72.60	$72.60
7 purchase totals =	$873.27		$964.8600	$964.87	$964.85	$964.80