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	$220.37	8.779%	$239.7163	$239.72	$239.70	$239.70
Purchase #2	$122.33	4.296%	$127.5853	$127.59	$127.60	$127.60
Purchase #3	$126.68	7.674%	$136.4014	$136.40	$136.40	$136.40
Purchase #4	$75.27	9.714%	$82.5817	$82.58	$82.60	$82.60
Purchase #5	$196.84	3.471%	$203.6723	$203.67	$203.65	$203.70
Purchase #6	$246.49	13.686%	$280.2246	$280.22	$280.20	$280.20
Purchase #7	$27.83	7.444%	$29.9017	$29.90	$29.90	$29.90
7 purchase totals =	$1,015.81		$1,100.0833	$1,100.08	$1,100.05	$1,100.10