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	$247.76	13.199%	$280.4618	$280.46	$280.45	$280.50
Purchase #2	$127.79	4.370%	$133.3744	$133.37	$133.35	$133.40
Purchase #3	$117.52	11.835%	$131.4285	$131.43	$131.45	$131.40
Purchase #4	$131.46	5.378%	$138.5299	$138.53	$138.55	$138.50
Purchase #5	$49.68	11.587%	$55.4364	$55.44	$55.45	$55.40
Purchase #6	$48.59	9.589%	$53.2493	$53.25	$53.25	$53.20
Purchase #7	$196.30	7.774%	$211.5604	$211.56	$211.55	$211.60
7 purchase totals =	$919.10		$1,004.0407	$1,004.04	$1,004.05	$1,004.00