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	$240.81	8.561%	$261.4257	$261.43	$261.45	$261.40
Purchase #2	$209.84	13.574%	$238.3237	$238.32	$238.30	$238.30
Purchase #3	$53.95	6.853%	$57.6472	$57.65	$57.65	$57.60
Purchase #4	$21.74	9.347%	$23.772	$23.77	$23.75	$23.80
Purchase #5	$236.37	9.267%	$258.2744	$258.27	$258.25	$258.30
Purchase #6	$99.95	11.651%	$111.5952	$111.60	$111.60	$111.60
Purchase #7	$34.64	10.492%	$38.2744	$38.27	$38.25	$38.30
7 purchase totals =	$897.30		$989.3126	$989.31	$989.25	$989.30