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	$76.33	8.717%	$82.9837	$82.98	$83.00	$83.00
Purchase #2	$86.93	4.280%	$90.6506	$90.65	$90.65	$90.70
Purchase #3	$20.80	3.641%	$21.5573	$21.56	$21.55	$21.60
Purchase #4	$207.93	8.414%	$225.4252	$225.43	$225.45	$225.40
Purchase #5	$128.45	4.571%	$134.3214	$134.32	$134.30	$134.30
Purchase #6	$41.43	7.285%	$44.4482	$44.45	$44.45	$44.40
Purchase #7	$38.59	12.639%	$43.4674	$43.47	$43.45	$43.50
7 purchase totals =	$600.46		$642.8538	$642.86	$642.85	$642.90