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	$25.89	8.195%	$28.0117	$28.01	$28.00	$28.00
Purchase #2	$249.78	3.473%	$258.4549	$258.45	$258.45	$258.50
Purchase #3	$100.97	3.581%	$104.5857	$104.59	$104.60	$104.60
Purchase #4	$120.86	5.352%	$127.3284	$127.33	$127.35	$127.30
Purchase #5	$104.77	3.819%	$108.7712	$108.77	$108.75	$108.80
Purchase #6	$59.87	9.264%	$65.4164	$65.42	$65.40	$65.40
Purchase #7	$182.43	9.418%	$199.6113	$199.61	$199.60	$199.60
7 purchase totals =	$844.57		$892.1796	$892.18	$892.15	$892.20