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	$224.79	13.760%	$255.7211	$255.72	$255.70	$255.70
Purchase #2	$63.39	3.543%	$65.6359	$65.64	$65.65	$65.60
Purchase #3	$78.35	12.874%	$88.4368	$88.44	$88.45	$88.40
Purchase #4	$146.78	6.592%	$156.4557	$156.46	$156.45	$156.50
Purchase #5	$171.76	13.174%	$194.3877	$194.39	$194.40	$194.40
Purchase #6	$6.76	13.230%	$7.6543	$7.65	$7.65	$7.70
Purchase #7	$170.99	8.838%	$186.1021	$186.10	$186.10	$186.10
7 purchase totals =	$862.82		$954.3936	$954.40	$954.40	$954.40