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	$55.75	6.647%	$59.4557	$59.46	$59.45	$59.50
Purchase #2	$59.96	6.455%	$63.8304	$63.83	$63.85	$63.80
Purchase #3	$125.96	8.456%	$136.6112	$136.61	$136.60	$136.60
Purchase #4	$100.72	6.803%	$107.572	$107.57	$107.55	$107.60
Purchase #5	$168.90	6.109%	$179.2181	$179.22	$179.20	$179.20
Purchase #6	$226.64	11.687%	$253.1274	$253.13	$253.15	$253.10
Purchase #7	$66.97	8.756%	$72.8339	$72.83	$72.85	$72.80
7 purchase totals =	$804.90		$872.6487	$872.65	$872.65	$872.60