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	$226.44	6.196%	$240.4702	$240.47	$240.45	$240.50
Purchase #2	$55.51	6.622%	$59.1859	$59.19	$59.20	$59.20
Purchase #3	$208.78	9.635%	$228.896	$228.90	$228.90	$228.90
Purchase #4	$124.42	7.748%	$134.0601	$134.06	$134.05	$134.10
Purchase #5	$115.40	6.819%	$123.2691	$123.27	$123.25	$123.30
Purchase #6	$184.84	5.156%	$194.3704	$194.37	$194.35	$194.40
Purchase #7	$55.43	12.751%	$62.4979	$62.50	$62.50	$62.50
7 purchase totals =	$970.82		$1,042.7496	$1,042.76	$1,042.70	$1,042.90