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	$142.43	12.667%	$160.4716	$160.47	$160.45	$160.50
Purchase #2	$99.60	10.533%	$110.0909	$110.09	$110.10	$110.10
Purchase #3	$56.87	5.660%	$60.0888	$60.09	$60.10	$60.10
Purchase #4	$145.33	5.624%	$153.5034	$153.50	$153.50	$153.50
Purchase #5	$37.75	10.434%	$41.6888	$41.69	$41.70	$41.70
Purchase #6	$123.61	9.114%	$134.8758	$134.88	$134.90	$134.90
Purchase #7	$250.47	12.478%	$281.7236	$281.72	$281.70	$281.70
7 purchase totals =	$856.06		$942.4429	$942.44	$942.45	$942.50