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	$242.44	5.218%	$255.0905	$255.09	$255.10	$255.10
Purchase #2	$48.80	7.606%	$52.5117	$52.51	$52.50	$52.50
Purchase #3	$131.48	10.373%	$145.1184	$145.12	$145.10	$145.10
Purchase #4	$30.59	9.271%	$33.426	$33.43	$33.45	$33.40
Purchase #5	$250.32	10.843%	$277.4622	$277.46	$277.45	$277.50
Purchase #6	$59.57	4.212%	$62.0791	$62.08	$62.10	$62.10
Purchase #7	$61.68	8.120%	$66.6884	$66.69	$66.70	$66.70
7 purchase totals =	$824.88		$892.3763	$892.38	$892.40	$892.40