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	$236.86	9.853%	$260.1978	$260.20	$260.20	$260.20
Purchase #2	$131.69	5.836%	$139.3754	$139.38	$139.40	$139.40
Purchase #3	$132.86	7.750%	$143.1567	$143.16	$143.15	$143.20
Purchase #4	$97.48	6.357%	$103.6768	$103.68	$103.70	$103.70
Purchase #5	$181.46	8.341%	$196.5956	$196.60	$196.60	$196.60
Purchase #6	$61.36	6.656%	$65.4441	$65.44	$65.45	$65.40
Purchase #7	$175.46	9.564%	$192.241	$192.24	$192.25	$192.20
7 purchase totals =	$1,017.17		$1,100.6874	$1,100.70	$1,100.75	$1,100.70