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	$121.93	4.269%	$127.1352	$127.14	$127.15	$127.10
Purchase #2	$237.65	12.724%	$267.8886	$267.89	$267.90	$267.90
Purchase #3	$18.35	6.802%	$19.5982	$19.60	$19.60	$19.60
Purchase #4	$185.70	5.515%	$195.9414	$195.94	$195.95	$195.90
Purchase #5	$95.31	3.859%	$98.988	$98.99	$99.00	$99.00
Purchase #6	$82.68	9.748%	$90.7396	$90.74	$90.75	$90.70
Purchase #7	$93.39	7.850%	$100.7211	$100.72	$100.70	$100.70
7 purchase totals =	$835.01		$901.0121	$901.02	$901.05	$900.90