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	$155.31	5.786%	$164.2962	$164.30	$164.30	$164.30
Purchase #2	$26.83	3.468%	$27.7605	$27.76	$27.75	$27.80
Purchase #3	$181.86	8.235%	$196.8362	$196.84	$196.85	$196.80
Purchase #4	$133.96	4.173%	$139.5502	$139.55	$139.55	$139.60
Purchase #5	$154.87	10.573%	$171.2444	$171.24	$171.25	$171.20
Purchase #6	$104.84	13.130%	$118.6055	$118.61	$118.60	$118.60
Purchase #7	$32.78	5.851%	$34.698	$34.70	$34.70	$34.70
7 purchase totals =	$790.45		$852.9910	$853.00	$853.00	$853.00