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	$240.82	11.661%	$268.902	$268.90	$268.90	$268.90
Purchase #2	$203.93	7.171%	$218.5538	$218.55	$218.55	$218.60
Purchase #3	$241.81	3.756%	$250.8924	$250.89	$250.90	$250.90
Purchase #4	$19.82	9.406%	$21.6843	$21.68	$21.70	$21.70
Purchase #5	$47.47	8.411%	$51.4627	$51.46	$51.45	$51.50
Purchase #6	$46.87	8.387%	$50.801	$50.80	$50.80	$50.80
Purchase #7	$37.69	5.536%	$39.7765	$39.78	$39.80	$39.80
7 purchase totals =	$838.41		$902.0727	$902.06	$902.10	$902.20