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	$225.82	3.686%	$234.1437	$234.14	$234.15	$234.10
Purchase #2	$133.25	9.340%	$145.6956	$145.70	$145.70	$145.70
Purchase #3	$176.73	13.105%	$199.8905	$199.89	$199.90	$199.90
Purchase #4	$63.80	12.715%	$71.9122	$71.91	$71.90	$71.90
Purchase #5	$242.93	7.108%	$260.1975	$260.20	$260.20	$260.20
Purchase #6	$76.39	6.774%	$81.5647	$81.56	$81.55	$81.60
Purchase #7	$82.54	9.286%	$90.2047	$90.20	$90.20	$90.20
7 purchase totals =	$1,001.46		$1,083.6089	$1,083.60	$1,083.60	$1,083.60