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	$240.56	6.166%	$255.3929	$255.39	$255.40	$255.40
Purchase #2	$205.78	9.354%	$225.0287	$225.03	$225.05	$225.00
Purchase #3	$160.68	11.161%	$178.6135	$178.61	$178.60	$178.60
Purchase #4	$177.59	7.674%	$191.2183	$191.22	$191.20	$191.20
Purchase #5	$82.71	8.540%	$89.7734	$89.77	$89.75	$89.80
Purchase #6	$35.42	9.430%	$38.7601	$38.76	$38.75	$38.80
Purchase #7	$231.35	12.140%	$259.4359	$259.44	$259.45	$259.40
7 purchase totals =	$1,134.09		$1,238.2228	$1,238.22	$1,238.20	$1,238.20