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	$78.39	6.389%	$83.3983	$83.40	$83.40	$83.40
Purchase #2	$245.97	6.354%	$261.5989	$261.60	$261.60	$261.60
Purchase #3	$36.72	6.408%	$39.073	$39.07	$39.05	$39.10
Purchase #4	$168.32	13.514%	$191.0668	$191.07	$191.05	$191.10
Purchase #5	$132.88	13.486%	$150.8002	$150.80	$150.80	$150.80
Purchase #6	$102.96	8.196%	$111.3986	$111.40	$111.40	$111.40
Purchase #7	$71.84	8.845%	$78.1942	$78.19	$78.20	$78.20
7 purchase totals =	$837.08		$915.5300	$915.53	$915.50	$915.60