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	$56.37	5.737%	$59.6039	$59.60	$59.60	$59.60
Purchase #2	$163.28	10.665%	$180.6938	$180.69	$180.70	$180.70
Purchase #3	$248.86	10.605%	$275.2516	$275.25	$275.25	$275.30
Purchase #4	$64.48	8.160%	$69.7416	$69.74	$69.75	$69.70
Purchase #5	$22.76	3.730%	$23.6089	$23.61	$23.60	$23.60
Purchase #6	$167.27	13.603%	$190.0237	$190.02	$190.00	$190.00
Purchase #7	$124.71	5.680%	$131.7935	$131.79	$131.80	$131.80
7 purchase totals =	$847.73		$930.7170	$930.70	$930.70	$930.70