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	$30.44	4.864%	$31.9206	$31.92	$31.90	$31.90
Purchase #2	$242.32	5.773%	$256.3091	$256.31	$256.30	$256.30
Purchase #3	$63.83	3.537%	$66.0877	$66.09	$66.10	$66.10
Purchase #4	$242.95	7.209%	$260.4643	$260.46	$260.45	$260.50
Purchase #5	$32.67	7.841%	$35.2317	$35.23	$35.25	$35.20
Purchase #6	$77.47	11.772%	$86.5898	$86.59	$86.60	$86.60
Purchase #7	$221.75	4.498%	$231.7243	$231.72	$231.70	$231.70
7 purchase totals =	$911.43		$968.3275	$968.32	$968.30	$968.30