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	$231.78	12.823%	$261.5011	$261.50	$261.50	$261.50
Purchase #2	$111.73	3.261%	$115.3735	$115.37	$115.35	$115.40
Purchase #3	$137.54	10.475%	$151.9473	$151.95	$151.95	$151.90
Purchase #4	$176.40	12.352%	$198.1889	$198.19	$198.20	$198.20
Purchase #5	$81.86	10.567%	$90.5101	$90.51	$90.50	$90.50
Purchase #6	$135.26	10.571%	$149.5583	$149.56	$149.55	$149.60
Purchase #7	$68.88	5.363%	$72.574	$72.57	$72.55	$72.60
7 purchase totals =	$943.45		$1,039.6532	$1,039.65	$1,039.60	$1,039.70