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	$75.55	3.297%	$78.0409	$78.04	$78.05	$78.00
Purchase #2	$66.64	11.538%	$74.3289	$74.33	$74.35	$74.30
Purchase #3	$139.85	9.114%	$152.5959	$152.60	$152.60	$152.60
Purchase #4	$153.59	13.638%	$174.5366	$174.54	$174.55	$174.50
Purchase #5	$76.35	13.576%	$86.7153	$86.72	$86.70	$86.70
Purchase #6	$147.78	12.622%	$166.4328	$166.43	$166.45	$166.40
Purchase #7	$173.63	11.677%	$193.9048	$193.90	$193.90	$193.90
7 purchase totals =	$833.39		$926.5552	$926.56	$926.60	$926.40