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	$76.86	7.652%	$82.7413	$82.74	$82.75	$82.70
Purchase #2	$133.61	4.440%	$139.5423	$139.54	$139.55	$139.50
Purchase #3	$105.28	13.671%	$119.6728	$119.67	$119.65	$119.70
Purchase #4	$112.86	4.198%	$117.5979	$117.60	$117.60	$117.60
Purchase #5	$12.48	6.427%	$13.2821	$13.28	$13.30	$13.30
Purchase #6	$142.30	9.127%	$155.2877	$155.29	$155.30	$155.30
Purchase #7	$207.43	3.705%	$215.1153	$215.12	$215.10	$215.10
7 purchase totals =	$790.82		$843.2394	$843.24	$843.25	$843.20