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	$85.63	13.840%	$97.4812	$97.48	$97.50	$97.50
Purchase #2	$128.42	6.189%	$136.3679	$136.37	$136.35	$136.40
Purchase #3	$98.38	3.772%	$102.0909	$102.09	$102.10	$102.10
Purchase #4	$102.30	9.241%	$111.7535	$111.75	$111.75	$111.80
Purchase #5	$45.39	11.748%	$50.7224	$50.72	$50.70	$50.70
Purchase #6	$80.51	11.334%	$89.635	$89.64	$89.65	$89.60
Purchase #7	$166.41	13.342%	$188.6124	$188.61	$188.60	$188.60
7 purchase totals =	$707.04		$776.6633	$776.66	$776.65	$776.70