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	$25.80	7.136%	$27.6411	$27.64	$27.65	$27.60
Purchase #2	$226.63	8.553%	$246.0137	$246.01	$246.00	$246.00
Purchase #3	$33.32	11.808%	$37.2544	$37.25	$37.25	$37.30
Purchase #4	$122.45	7.328%	$131.4231	$131.42	$131.40	$131.40
Purchase #5	$41.37	7.278%	$44.3809	$44.38	$44.40	$44.40
Purchase #6	$131.83	5.530%	$139.1202	$139.12	$139.10	$139.10
Purchase #7	$166.79	10.715%	$184.6615	$184.66	$184.65	$184.70
7 purchase totals =	$748.19		$810.4949	$810.48	$810.45	$810.50