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	$235.69	9.205%	$257.3853	$257.39	$257.40	$257.40
Purchase #2	$204.81	5.298%	$215.6608	$215.66	$215.65	$215.70
Purchase #3	$140.46	7.769%	$151.3723	$151.37	$151.35	$151.40
Purchase #4	$94.61	9.639%	$103.7295	$103.73	$103.75	$103.70
Purchase #5	$185.91	5.691%	$196.4901	$196.49	$196.50	$196.50
Purchase #6	$217.32	9.789%	$238.5935	$238.59	$238.60	$238.60
Purchase #7	$110.91	8.670%	$120.5259	$120.53	$120.55	$120.50
7 purchase totals =	$1,189.71		$1,283.7574	$1,283.76	$1,283.80	$1,283.80