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	$23.75	13.749%	$27.0154	$27.02	$27.00	$27.00
Purchase #2	$114.55	7.608%	$123.265	$123.27	$123.25	$123.30
Purchase #3	$76.38	11.586%	$85.2294	$85.23	$85.25	$85.20
Purchase #4	$166.46	5.379%	$175.4139	$175.41	$175.40	$175.40
Purchase #5	$119.48	6.619%	$127.3884	$127.39	$127.40	$127.40
Purchase #6	$248.40	9.425%	$271.8117	$271.81	$271.80	$271.80
Purchase #7	$79.62	10.619%	$88.0748	$88.07	$88.05	$88.10
7 purchase totals =	$828.64		$898.1986	$898.20	$898.15	$898.20