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	$237.96	13.563%	$270.2345	$270.23	$270.25	$270.20
Purchase #2	$65.44	12.196%	$73.4211	$73.42	$73.40	$73.40
Purchase #3	$60.35	11.281%	$67.1581	$67.16	$67.15	$67.20
Purchase #4	$38.71	4.540%	$40.4674	$40.47	$40.45	$40.50
Purchase #5	$13.90	10.206%	$15.3186	$15.32	$15.30	$15.30
Purchase #6	$95.45	8.223%	$103.2989	$103.30	$103.30	$103.30
Purchase #7	$92.93	4.353%	$96.9752	$96.98	$97.00	$97.00
7 purchase totals =	$604.74		$666.8738	$666.88	$666.85	$666.90