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	$42.80	6.386%	$45.5332	$45.53	$45.55	$45.50
Purchase #2	$246.38	10.568%	$272.4174	$272.42	$272.40	$272.40
Purchase #3	$162.52	13.782%	$184.9185	$184.92	$184.90	$184.90
Purchase #4	$49.68	11.270%	$55.2789	$55.28	$55.30	$55.30
Purchase #5	$161.84	8.504%	$175.6029	$175.60	$175.60	$175.60
Purchase #6	$102.73	6.826%	$109.7423	$109.74	$109.75	$109.70
Purchase #7	$239.51	6.261%	$254.5057	$254.51	$254.50	$254.50
7 purchase totals =	$1,005.46		$1,097.9989	$1,098.00	$1,098.00	$1,097.90