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	$246.82	7.504%	$265.3414	$265.34	$265.35	$265.30
Purchase #2	$57.77	3.172%	$59.6025	$59.60	$59.60	$59.60
Purchase #3	$66.28	7.758%	$71.422	$71.42	$71.40	$71.40
Purchase #4	$119.82	8.813%	$130.3797	$130.38	$130.40	$130.40
Purchase #5	$10.77	12.235%	$12.0877	$12.09	$12.10	$12.10
Purchase #6	$230.73	13.574%	$262.0493	$262.05	$262.05	$262.00
Purchase #7	$84.69	5.652%	$89.4767	$89.48	$89.50	$89.50
7 purchase totals =	$816.88		$890.3593	$890.36	$890.40	$890.30