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	$159.98	5.469%	$168.7293	$168.73	$168.75	$168.70
Purchase #2	$130.78	9.686%	$143.4474	$143.45	$143.45	$143.40
Purchase #3	$249.32	12.589%	$280.7069	$280.71	$280.70	$280.70
Purchase #4	$149.27	12.402%	$167.7825	$167.78	$167.80	$167.80
Purchase #5	$174.75	3.622%	$181.0794	$181.08	$181.10	$181.10
Purchase #6	$111.35	6.326%	$118.394	$118.39	$118.40	$118.40
Purchase #7	$233.33	11.159%	$259.3673	$259.37	$259.35	$259.40
7 purchase totals =	$1,208.78		$1,319.5068	$1,319.51	$1,319.55	$1,319.50