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	$154.77	7.509%	$166.3917	$166.39	$166.40	$166.40
Purchase #2	$178.56	6.809%	$190.7182	$190.72	$190.70	$190.70
Purchase #3	$176.76	10.184%	$194.7612	$194.76	$194.75	$194.80
Purchase #4	$94.32	3.607%	$97.7221	$97.72	$97.70	$97.70
Purchase #5	$30.25	12.627%	$34.0697	$34.07	$34.05	$34.10
Purchase #6	$98.59	6.681%	$105.1768	$105.18	$105.20	$105.20
Purchase #7	$30.42	5.406%	$32.0645	$32.06	$32.05	$32.10
7 purchase totals =	$763.67		$820.9042	$820.90	$820.85	$821.00