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	$136.98	10.102%	$150.8177	$150.82	$150.80	$150.80
Purchase #2	$228.26	13.219%	$258.4337	$258.43	$258.45	$258.40
Purchase #3	$130.42	6.403%	$138.7708	$138.77	$138.75	$138.80
Purchase #4	$184.61	8.198%	$199.7443	$199.74	$199.75	$199.70
Purchase #5	$106.51	4.601%	$111.4105	$111.41	$111.40	$111.40
Purchase #6	$41.55	3.815%	$43.1351	$43.14	$43.15	$43.10
Purchase #7	$92.43	6.465%	$98.4056	$98.41	$98.40	$98.40
7 purchase totals =	$920.76		$1,000.7177	$1,000.72	$1,000.70	$1,000.60