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	$84.45	6.387%	$89.8438	$89.84	$89.85	$89.80
Purchase #2	$93.81	12.659%	$105.6854	$105.69	$105.70	$105.70
Purchase #3	$122.87	11.298%	$136.7519	$136.75	$136.75	$136.80
Purchase #4	$106.25	3.239%	$109.6914	$109.69	$109.70	$109.70
Purchase #5	$93.58	10.789%	$103.6763	$103.68	$103.70	$103.70
Purchase #6	$228.25	5.690%	$241.2374	$241.24	$241.25	$241.20
Purchase #7	$82.88	12.760%	$93.4555	$93.46	$93.45	$93.50
7 purchase totals =	$812.09		$880.3417	$880.35	$880.40	$880.40