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	$44.87	12.711%	$50.5734	$50.57	$50.55	$50.60
Purchase #2	$248.28	13.364%	$281.4601	$281.46	$281.45	$281.50
Purchase #3	$141.37	9.858%	$155.3063	$155.31	$155.30	$155.30
Purchase #4	$200.94	12.720%	$226.4996	$226.50	$226.50	$226.50
Purchase #5	$69.65	9.728%	$76.4256	$76.43	$76.45	$76.40
Purchase #6	$120.38	3.713%	$124.8497	$124.85	$124.85	$124.80
Purchase #7	$137.43	10.253%	$151.5207	$151.52	$151.50	$151.50
7 purchase totals =	$962.92		$1,066.6354	$1,066.64	$1,066.60	$1,066.60