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	$137.70	4.295%	$143.6142	$143.61	$143.60	$143.60
Purchase #2	$128.86	6.167%	$136.8068	$136.81	$136.80	$136.80
Purchase #3	$57.94	10.260%	$63.8846	$63.88	$63.90	$63.90
Purchase #4	$52.44	9.261%	$57.2965	$57.30	$57.30	$57.30
Purchase #5	$194.55	11.845%	$217.5944	$217.59	$217.60	$217.60
Purchase #6	$71.92	9.494%	$78.7481	$78.75	$78.75	$78.70
Purchase #7	$60.94	7.302%	$65.3898	$65.39	$65.40	$65.40
7 purchase totals =	$704.35		$763.3344	$763.33	$763.35	$763.30