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	$238.72	13.473%	$270.8827	$270.88	$270.90	$270.90
Purchase #2	$153.93	4.264%	$160.4936	$160.49	$160.50	$160.50
Purchase #3	$211.56	6.395%	$225.0893	$225.09	$225.10	$225.10
Purchase #4	$13.94	13.667%	$15.8452	$15.85	$15.85	$15.80
Purchase #5	$115.40	10.246%	$127.2239	$127.22	$127.20	$127.20
Purchase #6	$205.37	9.475%	$224.8288	$224.83	$224.85	$224.80
Purchase #7	$159.48	6.506%	$169.8558	$169.86	$169.85	$169.90
7 purchase totals =	$1,098.40		$1,194.2193	$1,194.22	$1,194.25	$1,194.20