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	$55.55	7.155%	$59.5246	$59.52	$59.50	$59.50
Purchase #2	$112.95	6.496%	$120.2872	$120.29	$120.30	$120.30
Purchase #3	$66.28	8.546%	$71.9443	$71.94	$71.95	$71.90
Purchase #4	$147.43	9.760%	$161.8192	$161.82	$161.80	$161.80
Purchase #5	$22.90	7.860%	$24.6999	$24.70	$24.70	$24.70
Purchase #6	$107.55	4.672%	$112.5747	$112.57	$112.55	$112.60
Purchase #7	$89.49	5.726%	$94.6142	$94.61	$94.60	$94.60
7 purchase totals =	$602.15		$645.4641	$645.45	$645.40	$645.40