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	$25.85	6.359%	$27.4938	$27.49	$27.50	$27.50
Purchase #2	$135.64	5.113%	$142.5753	$142.58	$142.60	$142.60
Purchase #3	$11.71	13.671%	$13.3109	$13.31	$13.30	$13.30
Purchase #4	$214.59	13.439%	$243.4288	$243.43	$243.45	$243.40
Purchase #5	$167.61	3.687%	$173.7898	$173.79	$173.80	$173.80
Purchase #6	$76.45	6.481%	$81.4047	$81.40	$81.40	$81.40
Purchase #7	$240.30	9.377%	$262.8329	$262.83	$262.85	$262.80
7 purchase totals =	$872.15		$944.8362	$944.83	$944.90	$944.80