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	$38.38	9.610%	$42.0683	$42.07	$42.05	$42.10
Purchase #2	$38.97	4.655%	$40.7841	$40.78	$40.80	$40.80
Purchase #3	$236.40	6.451%	$251.6502	$251.65	$251.65	$251.70
Purchase #4	$133.72	12.632%	$150.6115	$150.61	$150.60	$150.60
Purchase #5	$89.43	3.729%	$92.7648	$92.76	$92.75	$92.80
Purchase #6	$163.72	9.374%	$179.0671	$179.07	$179.05	$179.10
Purchase #7	$40.85	5.407%	$43.0588	$43.06	$43.05	$43.10
7 purchase totals =	$741.47		$800.0048	$800.00	$799.95	$800.20