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	$205.52	8.171%	$222.313	$222.31	$222.30	$222.30
Purchase #2	$63.32	13.441%	$71.8308	$71.83	$71.85	$71.80
Purchase #3	$24.65	4.135%	$25.6693	$25.67	$25.65	$25.70
Purchase #4	$169.64	3.583%	$175.7182	$175.72	$175.70	$175.70
Purchase #5	$133.48	5.696%	$141.083	$141.08	$141.10	$141.10
Purchase #6	$30.89	7.129%	$33.0921	$33.09	$33.10	$33.10
Purchase #7	$144.31	11.232%	$160.5189	$160.52	$160.50	$160.50
7 purchase totals =	$771.81		$830.2253	$830.22	$830.20	$830.20