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	$99.52	9.609%	$109.0829	$109.08	$109.10	$109.10
Purchase #2	$20.80	3.820%	$21.5946	$21.59	$21.60	$21.60
Purchase #3	$11.45	9.537%	$12.542	$12.54	$12.55	$12.50
Purchase #4	$114.39	8.265%	$123.8443	$123.84	$123.85	$123.80
Purchase #5	$197.92	8.790%	$215.3172	$215.32	$215.30	$215.30
Purchase #6	$112.30	6.221%	$119.2862	$119.29	$119.30	$119.30
Purchase #7	$177.77	8.235%	$192.4094	$192.41	$192.40	$192.40
7 purchase totals =	$734.15		$794.0766	$794.07	$794.10	$794.00