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	$29.39	5.547%	$31.0203	$31.02	$31.00	$31.00
Purchase #2	$105.37	11.717%	$117.7162	$117.72	$117.70	$117.70
Purchase #3	$46.51	13.195%	$52.647	$52.65	$52.65	$52.60
Purchase #4	$73.49	6.132%	$77.9964	$78.00	$78.00	$78.00
Purchase #5	$137.78	13.734%	$156.7027	$156.70	$156.70	$156.70
Purchase #6	$152.34	10.578%	$168.4545	$168.45	$168.45	$168.50
Purchase #7	$145.65	4.490%	$152.1897	$152.19	$152.20	$152.20
7 purchase totals =	$690.53		$756.7268	$756.73	$756.70	$756.70