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	$127.72	9.482%	$139.8304	$139.83	$139.85	$139.80
Purchase #2	$55.76	7.493%	$59.9381	$59.94	$59.95	$59.90
Purchase #3	$17.51	10.653%	$19.3753	$19.38	$19.40	$19.40
Purchase #4	$120.57	3.561%	$124.8635	$124.86	$124.85	$124.90
Purchase #5	$236.68	5.751%	$250.2915	$250.29	$250.30	$250.30
Purchase #6	$129.86	10.145%	$143.0343	$143.03	$143.05	$143.00
Purchase #7	$181.71	13.668%	$206.5461	$206.55	$206.55	$206.50
7 purchase totals =	$869.81		$943.8792	$943.88	$943.95	$943.80