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	$168.98	13.373%	$191.5777	$191.58	$191.60	$191.60
Purchase #2	$219.45	6.532%	$233.7845	$233.78	$233.80	$233.80
Purchase #3	$233.77	9.744%	$256.5485	$256.55	$256.55	$256.50
Purchase #4	$178.83	3.787%	$185.6023	$185.60	$185.60	$185.60
Purchase #5	$12.66	12.201%	$14.2046	$14.20	$14.20	$14.20
Purchase #6	$139.28	6.416%	$148.2162	$148.22	$148.20	$148.20
Purchase #7	$44.83	12.174%	$50.2876	$50.29	$50.30	$50.30
7 purchase totals =	$997.80		$1,080.2214	$1,080.22	$1,080.25	$1,080.20