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	$246.26	3.203%	$254.1477	$254.15	$254.15	$254.10
Purchase #2	$18.26	12.754%	$20.5889	$20.59	$20.60	$20.60
Purchase #3	$242.93	12.341%	$272.91	$272.91	$272.90	$272.90
Purchase #4	$145.27	7.451%	$156.0941	$156.09	$156.10	$156.10
Purchase #5	$17.38	5.317%	$18.3041	$18.30	$18.30	$18.30
Purchase #6	$69.93	9.421%	$76.5181	$76.52	$76.50	$76.50
Purchase #7	$215.26	10.576%	$238.0259	$238.03	$238.05	$238.00
7 purchase totals =	$955.29		$1,036.5888	$1,036.59	$1,036.60	$1,036.50