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	$122.35	13.259%	$138.5724	$138.57	$138.55	$138.60
Purchase #2	$42.29	3.252%	$43.6653	$43.67	$43.65	$43.70
Purchase #3	$196.78	4.533%	$205.7	$205.70	$205.70	$205.70
Purchase #4	$175.82	10.771%	$194.7576	$194.76	$194.75	$194.80
Purchase #5	$189.50	11.139%	$210.6084	$210.61	$210.60	$210.60
Purchase #6	$95.42	11.341%	$106.2416	$106.24	$106.25	$106.20
Purchase #7	$142.66	5.742%	$150.8515	$150.85	$150.85	$150.90
7 purchase totals =	$964.82		$1,050.3968	$1,050.40	$1,050.35	$1,050.50