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	$26.63	3.349%	$27.5218	$27.52	$27.50	$27.50
Purchase #2	$224.85	13.776%	$255.8253	$255.83	$255.85	$255.80
Purchase #3	$208.58	4.686%	$218.3541	$218.35	$218.35	$218.40
Purchase #4	$104.48	6.709%	$111.4896	$111.49	$111.50	$111.50
Purchase #5	$136.93	6.107%	$145.2923	$145.29	$145.30	$145.30
Purchase #6	$191.28	13.859%	$217.7895	$217.79	$217.80	$217.80
Purchase #7	$109.37	8.140%	$118.2727	$118.27	$118.25	$118.30
7 purchase totals =	$1,002.12		$1,094.5453	$1,094.54	$1,094.55	$1,094.60