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	$102.34	12.685%	$115.3218	$115.32	$115.30	$115.30
Purchase #2	$51.76	10.845%	$57.3734	$57.37	$57.35	$57.40
Purchase #3	$144.30	4.230%	$150.4039	$150.40	$150.40	$150.40
Purchase #4	$128.59	10.868%	$142.5652	$142.57	$142.55	$142.60
Purchase #5	$25.62	6.187%	$27.2051	$27.21	$27.20	$27.20
Purchase #6	$189.97	5.570%	$200.5513	$200.55	$200.55	$200.60
Purchase #7	$250.37	5.249%	$263.5119	$263.51	$263.50	$263.50
7 purchase totals =	$892.95		$956.9326	$956.93	$956.85	$957.00