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	$19.97	7.659%	$21.4995	$21.50	$21.50	$21.50
Purchase #2	$19.60	8.769%	$21.3187	$21.32	$21.30	$21.30
Purchase #3	$106.58	7.344%	$114.4072	$114.41	$114.40	$114.40
Purchase #4	$63.96	11.315%	$71.1971	$71.20	$71.20	$71.20
Purchase #5	$182.72	13.836%	$208.0011	$208.00	$208.00	$208.00
Purchase #6	$109.41	12.868%	$123.4889	$123.49	$123.50	$123.50
Purchase #7	$83.88	6.495%	$89.328	$89.33	$89.35	$89.30
7 purchase totals =	$586.12		$649.2405	$649.25	$649.25	$649.20