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	$223.36	12.457%	$251.184	$251.18	$251.20	$251.20
Purchase #2	$37.52	10.450%	$41.4408	$41.44	$41.45	$41.40
Purchase #3	$137.63	6.813%	$147.0067	$147.01	$147.00	$147.00
Purchase #4	$128.52	7.322%	$137.9302	$137.93	$137.95	$137.90
Purchase #5	$82.50	3.660%	$85.5195	$85.52	$85.50	$85.50
Purchase #6	$126.85	13.772%	$144.3198	$144.32	$144.30	$144.30
Purchase #7	$190.45	4.679%	$199.3612	$199.36	$199.35	$199.40
7 purchase totals =	$926.83		$1,006.7622	$1,006.76	$1,006.75	$1,006.70