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	$178.49	6.109%	$189.394	$189.39	$189.40	$189.40
Purchase #2	$143.39	10.659%	$158.6739	$158.67	$158.65	$158.70
Purchase #3	$92.80	7.637%	$99.8871	$99.89	$99.90	$99.90
Purchase #4	$180.82	13.393%	$205.0372	$205.04	$205.05	$205.00
Purchase #5	$194.79	4.846%	$204.2295	$204.23	$204.25	$204.20
Purchase #6	$81.77	9.710%	$89.7099	$89.71	$89.70	$89.70
Purchase #7	$123.59	12.161%	$138.6198	$138.62	$138.60	$138.60
7 purchase totals =	$995.65		$1,085.5514	$1,085.55	$1,085.55	$1,085.50