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	$21.27	7.640%	$22.895	$22.90	$22.90	$22.90
Purchase #2	$53.81	10.789%	$59.6156	$59.62	$59.60	$59.60
Purchase #3	$54.62	9.513%	$59.816	$59.82	$59.80	$59.80
Purchase #4	$200.50	12.127%	$224.8146	$224.81	$224.80	$224.80
Purchase #5	$29.67	6.646%	$31.6419	$31.64	$31.65	$31.60
Purchase #6	$152.97	6.699%	$163.2175	$163.22	$163.20	$163.20
Purchase #7	$55.82	6.350%	$59.3646	$59.36	$59.35	$59.40
7 purchase totals =	$568.66		$621.3652	$621.37	$621.30	$621.30