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	$244.30	8.709%	$265.5761	$265.58	$265.60	$265.60
Purchase #2	$62.71	10.592%	$69.3522	$69.35	$69.35	$69.40
Purchase #3	$156.55	3.174%	$161.5189	$161.52	$161.50	$161.50
Purchase #4	$189.98	13.853%	$216.2979	$216.30	$216.30	$216.30
Purchase #5	$156.46	3.847%	$162.479	$162.48	$162.50	$162.50
Purchase #6	$183.31	13.694%	$208.4125	$208.41	$208.40	$208.40
Purchase #7	$178.25	10.188%	$196.4101	$196.41	$196.40	$196.40
7 purchase totals =	$1,171.56		$1,280.0467	$1,280.05	$1,280.05	$1,280.10