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	$36.83	13.106%	$41.6569	$41.66	$41.65	$41.70
Purchase #2	$168.80	5.406%	$177.9253	$177.93	$177.95	$177.90
Purchase #3	$61.70	7.292%	$66.1992	$66.20	$66.20	$66.20
Purchase #4	$161.25	3.802%	$167.3807	$167.38	$167.40	$167.40
Purchase #5	$174.87	9.482%	$191.4512	$191.45	$191.45	$191.50
Purchase #6	$104.28	7.289%	$111.881	$111.88	$111.90	$111.90
Purchase #7	$109.73	4.699%	$114.8862	$114.89	$114.90	$114.90
7 purchase totals =	$817.46		$871.3805	$871.39	$871.45	$871.50