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	$12.58	7.467%	$13.5193	$13.52	$13.50	$13.50
Purchase #2	$134.47	5.170%	$141.4221	$141.42	$141.40	$141.40
Purchase #3	$220.47	3.217%	$227.5625	$227.56	$227.55	$227.60
Purchase #4	$171.77	9.625%	$188.3029	$188.30	$188.30	$188.30
Purchase #5	$52.90	8.270%	$57.2748	$57.27	$57.25	$57.30
Purchase #6	$141.46	10.751%	$156.6684	$156.67	$156.65	$156.70
Purchase #7	$184.72	3.172%	$190.5793	$190.58	$190.60	$190.60
7 purchase totals =	$918.37		$975.3293	$975.32	$975.25	$975.40