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	$222.62	10.624%	$246.2711	$246.27	$246.25	$246.30
Purchase #2	$61.37	10.849%	$68.028	$68.03	$68.05	$68.00
Purchase #3	$65.64	10.519%	$72.5447	$72.54	$72.55	$72.50
Purchase #4	$17.96	12.442%	$20.1946	$20.19	$20.20	$20.20
Purchase #5	$46.68	13.670%	$53.0612	$53.06	$53.05	$53.10
Purchase #6	$42.25	8.724%	$45.9359	$45.94	$45.95	$45.90
Purchase #7	$13.26	11.783%	$14.8224	$14.82	$14.80	$14.80
7 purchase totals =	$469.78		$520.8579	$520.85	$520.85	$520.80