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	$90.77	8.417%	$98.4101	$98.41	$98.40	$98.40
Purchase #2	$37.87	4.452%	$39.556	$39.56	$39.55	$39.60
Purchase #3	$21.75	6.379%	$23.1374	$23.14	$23.15	$23.10
Purchase #4	$189.84	3.304%	$196.1123	$196.11	$196.10	$196.10
Purchase #5	$140.51	12.634%	$158.262	$158.26	$158.25	$158.30
Purchase #6	$141.50	12.731%	$159.5144	$159.51	$159.50	$159.50
Purchase #7	$178.83	6.731%	$190.867	$190.87	$190.85	$190.90
7 purchase totals =	$801.07		$865.8592	$865.86	$865.80	$865.90