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	$242.47	7.396%	$260.4031	$260.40	$260.40	$260.40
Purchase #2	$93.61	13.313%	$106.0723	$106.07	$106.05	$106.10
Purchase #3	$28.55	13.186%	$32.3146	$32.31	$32.30	$32.30
Purchase #4	$29.84	11.757%	$33.3483	$33.35	$33.35	$33.30
Purchase #5	$77.63	10.524%	$85.7998	$85.80	$85.80	$85.80
Purchase #6	$59.45	13.646%	$67.5625	$67.56	$67.55	$67.60
Purchase #7	$141.61	8.318%	$153.3891	$153.39	$153.40	$153.40
7 purchase totals =	$673.16		$738.8897	$738.88	$738.85	$738.90