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	$125.66	10.524%	$138.8845	$138.88	$138.90	$138.90
Purchase #2	$207.47	10.305%	$228.8498	$228.85	$228.85	$228.80
Purchase #3	$71.96	9.584%	$78.8566	$78.86	$78.85	$78.90
Purchase #4	$132.94	3.358%	$137.4041	$137.40	$137.40	$137.40
Purchase #5	$28.31	9.856%	$31.1002	$31.10	$31.10	$31.10
Purchase #6	$29.54	6.154%	$31.3579	$31.36	$31.35	$31.40
Purchase #7	$27.81	4.341%	$29.0172	$29.02	$29.00	$29.00
7 purchase totals =	$623.69		$675.4703	$675.47	$675.45	$675.50