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	$143.42	11.481%	$159.8861	$159.89	$159.90	$159.90
Purchase #2	$94.58	4.108%	$98.4653	$98.47	$98.45	$98.50
Purchase #3	$184.44	11.676%	$205.9752	$205.98	$206.00	$206.00
Purchase #4	$241.66	9.628%	$264.927	$264.93	$264.95	$264.90
Purchase #5	$25.40	10.801%	$28.1435	$28.14	$28.15	$28.10
Purchase #6	$211.64	5.661%	$223.6209	$223.62	$223.60	$223.60
Purchase #7	$127.31	10.324%	$140.4535	$140.45	$140.45	$140.50
7 purchase totals =	$1,028.45		$1,121.4715	$1,121.48	$1,121.50	$1,121.50