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	$49.84	9.524%	$54.5868	$54.59	$54.60	$54.60
Purchase #2	$69.26	12.813%	$78.1343	$78.13	$78.15	$78.10
Purchase #3	$176.28	8.231%	$190.7896	$190.79	$190.80	$190.80
Purchase #4	$107.36	5.200%	$112.9427	$112.94	$112.95	$112.90
Purchase #5	$45.97	11.526%	$51.2685	$51.27	$51.25	$51.30
Purchase #6	$32.34	3.107%	$33.3448	$33.34	$33.35	$33.30
Purchase #7	$64.48	6.809%	$68.8704	$68.87	$68.85	$68.90
7 purchase totals =	$545.53		$589.9371	$589.93	$589.95	$589.90