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	$21.74	13.298%	$24.631	$24.63	$24.65	$24.60
Purchase #2	$71.57	9.713%	$78.5216	$78.52	$78.50	$78.50
Purchase #3	$168.51	5.159%	$177.2034	$177.20	$177.20	$177.20
Purchase #4	$205.61	11.461%	$229.175	$229.18	$229.20	$229.20
Purchase #5	$185.56	5.693%	$196.1239	$196.12	$196.10	$196.10
Purchase #6	$23.94	12.198%	$26.8602	$26.86	$26.85	$26.90
Purchase #7	$196.50	11.690%	$219.4709	$219.47	$219.45	$219.50
7 purchase totals =	$873.43		$951.9860	$951.98	$951.95	$952.00