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	$135.86	13.778%	$154.5788	$154.58	$154.60	$154.60
Purchase #2	$161.88	12.743%	$182.5084	$182.51	$182.50	$182.50
Purchase #3	$116.41	10.726%	$128.8961	$128.90	$128.90	$128.90
Purchase #4	$52.85	11.715%	$59.0414	$59.04	$59.05	$59.00
Purchase #5	$162.65	11.692%	$181.667	$181.67	$181.65	$181.70
Purchase #6	$44.84	12.509%	$50.449	$50.45	$50.45	$50.40
Purchase #7	$182.84	12.114%	$204.9892	$204.99	$205.00	$205.00
7 purchase totals =	$857.33		$962.1299	$962.14	$962.15	$962.10