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	$42.85	10.760%	$47.4607	$47.46	$47.45	$47.50
Purchase #2	$81.60	4.794%	$85.5119	$85.51	$85.50	$85.50
Purchase #3	$219.36	9.554%	$240.3177	$240.32	$240.30	$240.30
Purchase #4	$131.91	11.238%	$146.734	$146.73	$146.75	$146.70
Purchase #5	$129.98	10.659%	$143.8346	$143.83	$143.85	$143.80
Purchase #6	$44.95	6.670%	$47.9482	$47.95	$47.95	$47.90
Purchase #7	$34.57	10.395%	$38.1636	$38.16	$38.15	$38.20
7 purchase totals =	$685.22		$749.9707	$749.96	$749.95	$749.90