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	$126.67	4.116%	$131.8837	$131.88	$131.90	$131.90
Purchase #2	$167.70	10.340%	$185.0402	$185.04	$185.05	$185.00
Purchase #3	$23.43	8.672%	$25.4618	$25.46	$25.45	$25.50
Purchase #4	$121.26	10.105%	$133.5133	$133.51	$133.50	$133.50
Purchase #5	$124.27	9.654%	$136.267	$136.27	$136.25	$136.30
Purchase #6	$123.84	12.317%	$139.0934	$139.09	$139.10	$139.10
Purchase #7	$43.65	11.459%	$48.6519	$48.65	$48.65	$48.70
7 purchase totals =	$730.82		$799.9113	$799.90	$799.90	$800.00