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	$116.39	6.392%	$123.8296	$123.83	$123.85	$123.80
Purchase #2	$97.62	4.741%	$102.2482	$102.25	$102.25	$102.20
Purchase #3	$123.86	6.123%	$131.4439	$131.44	$131.45	$131.40
Purchase #4	$46.76	3.192%	$48.2526	$48.25	$48.25	$48.30
Purchase #5	$77.79	10.206%	$85.7292	$85.73	$85.75	$85.70
Purchase #6	$228.26	13.295%	$258.6072	$258.61	$258.60	$258.60
Purchase #7	$48.98	12.159%	$54.9355	$54.94	$54.95	$54.90
7 purchase totals =	$739.66		$805.0462	$805.05	$805.10	$804.90