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	$20.94	11.512%	$23.3506	$23.35	$23.35	$23.40
Purchase #2	$106.45	4.467%	$111.2051	$111.21	$111.20	$111.20
Purchase #3	$39.40	5.256%	$41.4709	$41.47	$41.45	$41.50
Purchase #4	$126.29	4.402%	$131.8493	$131.85	$131.85	$131.80
Purchase #5	$99.84	5.782%	$105.6127	$105.61	$105.60	$105.60
Purchase #6	$219.96	10.648%	$243.3813	$243.38	$243.40	$243.40
Purchase #7	$31.73	6.236%	$33.7087	$33.71	$33.70	$33.70
7 purchase totals =	$644.61		$690.5786	$690.58	$690.55	$690.60