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	$56.45	5.312%	$59.4486	$59.45	$59.45	$59.40
Purchase #2	$112.88	3.622%	$116.9685	$116.97	$116.95	$117.00
Purchase #3	$123.32	10.511%	$136.2822	$136.28	$136.30	$136.30
Purchase #4	$156.25	11.702%	$174.5344	$174.53	$174.55	$174.50
Purchase #5	$250.98	7.227%	$269.1183	$269.12	$269.10	$269.10
Purchase #6	$123.40	3.800%	$128.0892	$128.09	$128.10	$128.10
Purchase #7	$68.91	6.434%	$73.3437	$73.34	$73.35	$73.30
7 purchase totals =	$892.19		$957.7849	$957.78	$957.80	$957.70