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	$249.99	12.201%	$280.4913	$280.49	$280.50	$280.50
Purchase #2	$191.57	12.670%	$215.8419	$215.84	$215.85	$215.80
Purchase #3	$48.30	12.753%	$54.4597	$54.46	$54.45	$54.50
Purchase #4	$145.82	9.796%	$160.1045	$160.10	$160.10	$160.10
Purchase #5	$102.81	13.583%	$116.7747	$116.77	$116.75	$116.80
Purchase #6	$120.43	5.462%	$127.0079	$127.01	$127.00	$127.00
Purchase #7	$147.56	5.783%	$156.0934	$156.09	$156.10	$156.10
7 purchase totals =	$1,006.48		$1,110.7734	$1,110.76	$1,110.75	$1,110.80