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	$63.90	5.192%	$67.2177	$67.22	$67.20	$67.20
Purchase #2	$231.81	11.422%	$258.2873	$258.29	$258.30	$258.30
Purchase #3	$21.78	6.814%	$23.2641	$23.26	$23.25	$23.30
Purchase #4	$134.59	3.719%	$139.5954	$139.60	$139.60	$139.60
Purchase #5	$174.46	13.516%	$198.04	$198.04	$198.05	$198.00
Purchase #6	$204.60	13.197%	$231.6011	$231.60	$231.60	$231.60
Purchase #7	$246.90	3.431%	$255.3711	$255.37	$255.35	$255.40
7 purchase totals =	$1,078.04		$1,173.3767	$1,173.38	$1,173.35	$1,173.40