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	$11.39	12.699%	$12.8364	$12.84	$12.85	$12.80
Purchase #2	$42.88	13.230%	$48.553	$48.55	$48.55	$48.60
Purchase #3	$118.42	7.532%	$127.3394	$127.34	$127.35	$127.30
Purchase #4	$118.51	4.115%	$123.3867	$123.39	$123.40	$123.40
Purchase #5	$71.54	5.669%	$75.5956	$75.60	$75.60	$75.60
Purchase #6	$47.70	6.300%	$50.7051	$50.71	$50.70	$50.70
Purchase #7	$156.87	9.298%	$171.4558	$171.46	$171.45	$171.50
7 purchase totals =	$567.31		$609.8720	$609.89	$609.90	$609.90