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	$202.89	8.149%	$219.4235	$219.42	$219.40	$219.40
Purchase #2	$134.30	7.182%	$143.9454	$143.95	$143.95	$143.90
Purchase #3	$231.98	9.279%	$253.5054	$253.51	$253.50	$253.50
Purchase #4	$183.87	6.321%	$195.4924	$195.49	$195.50	$195.50
Purchase #5	$48.88	4.791%	$51.2218	$51.22	$51.20	$51.20
Purchase #6	$184.96	3.714%	$191.8294	$191.83	$191.85	$191.80
Purchase #7	$29.59	6.294%	$31.4524	$31.45	$31.45	$31.50
7 purchase totals =	$1,016.47		$1,086.8703	$1,086.87	$1,086.85	$1,086.80