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	$111.89	8.685%	$121.6076	$121.61	$121.60	$121.60
Purchase #2	$65.25	13.815%	$74.2643	$74.26	$74.25	$74.30
Purchase #3	$120.25	6.679%	$128.2815	$128.28	$128.30	$128.30
Purchase #4	$233.85	12.685%	$263.5139	$263.51	$263.50	$263.50
Purchase #5	$57.90	13.820%	$65.9018	$65.90	$65.90	$65.90
Purchase #6	$247.62	10.494%	$273.6052	$273.61	$273.60	$273.60
Purchase #7	$189.33	3.710%	$196.3541	$196.35	$196.35	$196.40
7 purchase totals =	$1,026.09		$1,123.5284	$1,123.52	$1,123.50	$1,123.60