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	$36.38	10.222%	$40.0988	$40.10	$40.10	$40.10
Purchase #2	$222.44	4.815%	$233.1505	$233.15	$233.15	$233.20
Purchase #3	$65.84	10.353%	$72.6564	$72.66	$72.65	$72.70
Purchase #4	$16.54	6.733%	$17.6536	$17.65	$17.65	$17.70
Purchase #5	$158.72	8.279%	$171.8604	$171.86	$171.85	$171.90
Purchase #6	$233.94	5.509%	$246.8278	$246.83	$246.85	$246.80
Purchase #7	$218.85	3.817%	$227.2035	$227.20	$227.20	$227.20
7 purchase totals =	$952.71		$1,009.4510	$1,009.45	$1,009.45	$1,009.60