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	$139.97	12.385%	$157.3053	$157.31	$157.30	$157.30
Purchase #2	$177.55	12.426%	$199.6124	$199.61	$199.60	$199.60
Purchase #3	$59.61	11.553%	$66.4967	$66.50	$66.50	$66.50
Purchase #4	$130.58	10.311%	$144.0441	$144.04	$144.05	$144.00
Purchase #5	$220.31	7.664%	$237.1946	$237.19	$237.20	$237.20
Purchase #6	$148.82	4.408%	$155.38	$155.38	$155.40	$155.40
Purchase #7	$181.39	8.204%	$196.2712	$196.27	$196.25	$196.30
7 purchase totals =	$1,058.23		$1,156.3043	$1,156.30	$1,156.30	$1,156.30