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	$15.57	12.208%	$17.4708	$17.47	$17.45	$17.50
Purchase #2	$99.27	10.298%	$109.4928	$109.49	$109.50	$109.50
Purchase #3	$242.31	4.656%	$253.592	$253.59	$253.60	$253.60
Purchase #4	$154.39	8.853%	$168.0581	$168.06	$168.05	$168.10
Purchase #5	$85.95	6.522%	$91.5557	$91.56	$91.55	$91.60
Purchase #6	$71.40	3.228%	$73.7048	$73.70	$73.70	$73.70
Purchase #7	$178.54	5.143%	$187.7223	$187.72	$187.70	$187.70
7 purchase totals =	$847.43		$901.5965	$901.59	$901.55	$901.70