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	$20.75	13.467%	$23.5444	$23.54	$23.55	$23.50
Purchase #2	$14.89	3.663%	$15.4354	$15.44	$15.45	$15.40
Purchase #3	$130.38	9.649%	$142.9604	$142.96	$142.95	$143.00
Purchase #4	$245.64	6.871%	$262.5179	$262.52	$262.50	$262.50
Purchase #5	$99.85	4.778%	$104.6208	$104.62	$104.60	$104.60
Purchase #6	$210.39	11.700%	$235.0056	$235.01	$235.00	$235.00
Purchase #7	$189.27	3.568%	$196.0232	$196.02	$196.00	$196.00
7 purchase totals =	$911.17		$980.1077	$980.11	$980.05	$980.00