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	$104.72	6.448%	$111.4723	$111.47	$111.45	$111.50
Purchase #2	$124.60	3.398%	$128.8339	$128.83	$128.85	$128.80
Purchase #3	$196.53	11.182%	$218.506	$218.51	$218.50	$218.50
Purchase #4	$35.84	8.292%	$38.8119	$38.81	$38.80	$38.80
Purchase #5	$232.43	13.488%	$263.7802	$263.78	$263.80	$263.80
Purchase #6	$32.25	9.377%	$35.2741	$35.27	$35.25	$35.30
Purchase #7	$54.80	9.605%	$60.0635	$60.06	$60.05	$60.10
7 purchase totals =	$781.17		$856.7419	$856.73	$856.70	$856.80