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	$66.42	9.586%	$72.787	$72.79	$72.80	$72.80
Purchase #2	$35.36	13.423%	$40.1064	$40.11	$40.10	$40.10
Purchase #3	$62.55	6.307%	$66.495	$66.50	$66.50	$66.50
Purchase #4	$190.48	3.398%	$196.9525	$196.95	$196.95	$197.00
Purchase #5	$146.91	5.472%	$154.9489	$154.95	$154.95	$154.90
Purchase #6	$111.55	10.796%	$123.5929	$123.59	$123.60	$123.60
Purchase #7	$235.85	13.523%	$267.744	$267.74	$267.75	$267.70
7 purchase totals =	$849.12		$922.6267	$922.63	$922.65	$922.60