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	$250.25	7.409%	$268.791	$268.79	$268.80	$268.80
Purchase #2	$121.57	13.218%	$137.6391	$137.64	$137.65	$137.60
Purchase #3	$229.28	3.397%	$237.0686	$237.07	$237.05	$237.10
Purchase #4	$147.42	13.188%	$166.8617	$166.86	$166.85	$166.90
Purchase #5	$155.67	11.140%	$173.0116	$173.01	$173.00	$173.00
Purchase #6	$12.34	9.796%	$13.5488	$13.55	$13.55	$13.50
Purchase #7	$53.46	11.353%	$59.5293	$59.53	$59.55	$59.50
7 purchase totals =	$969.99		$1,056.4501	$1,056.45	$1,056.45	$1,056.40