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	$19.63	4.480%	$20.5094	$20.51	$20.50	$20.50
Purchase #2	$155.99	6.513%	$166.1496	$166.15	$166.15	$166.10
Purchase #3	$198.43	13.611%	$225.4383	$225.44	$225.45	$225.40
Purchase #4	$30.82	9.862%	$33.8595	$33.86	$33.85	$33.90
Purchase #5	$39.81	5.622%	$42.0481	$42.05	$42.05	$42.00
Purchase #6	$200.79	12.851%	$226.5935	$226.59	$226.60	$226.60
Purchase #7	$80.97	12.536%	$91.1204	$91.12	$91.10	$91.10
7 purchase totals =	$726.44		$805.7188	$805.72	$805.70	$805.60