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	$248.38	10.417%	$274.2537	$274.25	$274.25	$274.30
Purchase #2	$68.37	5.418%	$72.0743	$72.07	$72.05	$72.10
Purchase #3	$200.56	5.660%	$211.9117	$211.91	$211.90	$211.90
Purchase #4	$117.46	5.697%	$124.1517	$124.15	$124.15	$124.20
Purchase #5	$52.72	4.611%	$55.1509	$55.15	$55.15	$55.20
Purchase #6	$17.94	13.572%	$20.3748	$20.37	$20.35	$20.40
Purchase #7	$88.61	7.610%	$95.3532	$95.35	$95.35	$95.40
7 purchase totals =	$794.04		$853.2703	$853.25	$853.20	$853.50