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	$161.62	4.388%	$168.7119	$168.71	$168.70	$168.70
Purchase #2	$54.72	3.263%	$56.5055	$56.51	$56.50	$56.50
Purchase #3	$134.26	9.167%	$146.5676	$146.57	$146.55	$146.60
Purchase #4	$206.60	5.606%	$218.182	$218.18	$218.20	$218.20
Purchase #5	$191.34	11.591%	$213.5182	$213.52	$213.50	$213.50
Purchase #6	$33.59	12.729%	$37.8657	$37.87	$37.85	$37.90
Purchase #7	$71.88	9.390%	$78.6295	$78.63	$78.65	$78.60
7 purchase totals =	$854.01		$919.9804	$919.99	$919.95	$920.00