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	$49.82	13.397%	$56.4944	$56.49	$56.50	$56.50
Purchase #2	$37.76	12.141%	$42.3444	$42.34	$42.35	$42.30
Purchase #3	$157.89	8.571%	$171.4228	$171.42	$171.40	$171.40
Purchase #4	$247.60	13.241%	$280.3847	$280.38	$280.40	$280.40
Purchase #5	$226.74	12.754%	$255.6584	$255.66	$255.65	$255.70
Purchase #6	$175.96	7.774%	$189.6391	$189.64	$189.65	$189.60
Purchase #7	$113.31	9.194%	$123.7277	$123.73	$123.75	$123.70
7 purchase totals =	$1,009.08		$1,119.6715	$1,119.66	$1,119.70	$1,119.60