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	$142.30	6.520%	$151.578	$151.58	$151.60	$151.60
Purchase #2	$99.71	11.677%	$111.3531	$111.35	$111.35	$111.40
Purchase #3	$169.49	13.215%	$191.8881	$191.89	$191.90	$191.90
Purchase #4	$207.79	7.287%	$222.9317	$222.93	$222.95	$222.90
Purchase #5	$115.86	5.747%	$122.5185	$122.52	$122.50	$122.50
Purchase #6	$8.70	10.166%	$9.5844	$9.58	$9.60	$9.60
Purchase #7	$31.27	13.689%	$35.5506	$35.55	$35.55	$35.60
7 purchase totals =	$775.12		$845.4044	$845.40	$845.45	$845.50