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	$214.27	3.190%	$221.1052	$221.11	$221.10	$221.10
Purchase #2	$117.74	5.685%	$124.4335	$124.43	$124.45	$124.40
Purchase #3	$162.53	10.630%	$179.8069	$179.81	$179.80	$179.80
Purchase #4	$208.32	9.309%	$227.7125	$227.71	$227.70	$227.70
Purchase #5	$131.50	12.558%	$148.0138	$148.01	$148.00	$148.00
Purchase #6	$83.97	12.448%	$94.4226	$94.42	$94.40	$94.40
Purchase #7	$86.86	4.255%	$90.5559	$90.56	$90.55	$90.60
7 purchase totals =	$1,005.19		$1,086.0504	$1,086.05	$1,086.00	$1,086.00