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	$133.76	8.409%	$145.0079	$145.01	$145.00	$145.00
Purchase #2	$154.51	12.426%	$173.7094	$173.71	$173.70	$173.70
Purchase #3	$40.38	7.283%	$43.3209	$43.32	$43.30	$43.30
Purchase #4	$39.69	8.152%	$42.9255	$42.93	$42.95	$42.90
Purchase #5	$217.70	4.283%	$227.0241	$227.02	$227.00	$227.00
Purchase #6	$34.56	8.155%	$37.3784	$37.38	$37.40	$37.40
Purchase #7	$199.89	10.293%	$220.4647	$220.46	$220.45	$220.50
7 purchase totals =	$820.49		$889.8309	$889.83	$889.80	$889.80