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	$87.77	7.688%	$94.5178	$94.52	$94.50	$94.50
Purchase #2	$141.93	6.363%	$150.961	$150.96	$150.95	$151.00
Purchase #3	$20.30	5.721%	$21.4614	$21.46	$21.45	$21.50
Purchase #4	$146.37	13.209%	$165.704	$165.70	$165.70	$165.70
Purchase #5	$232.67	10.242%	$256.5001	$256.50	$256.50	$256.50
Purchase #6	$148.81	4.650%	$155.7297	$155.73	$155.75	$155.70
Purchase #7	$137.54	6.109%	$145.9423	$145.94	$145.95	$145.90
7 purchase totals =	$915.39		$990.8163	$990.81	$990.80	$990.80