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	$219.83	5.157%	$231.1666	$231.17	$231.15	$231.20
Purchase #2	$177.57	12.824%	$200.3416	$200.34	$200.35	$200.30
Purchase #3	$92.74	11.809%	$103.6917	$103.69	$103.70	$103.70
Purchase #4	$95.61	4.570%	$99.9794	$99.98	$100.00	$100.00
Purchase #5	$118.61	6.861%	$126.7478	$126.75	$126.75	$126.70
Purchase #6	$9.74	4.155%	$10.1447	$10.14	$10.15	$10.10
Purchase #7	$46.59	9.184%	$50.8688	$50.87	$50.85	$50.90
7 purchase totals =	$760.69		$822.9406	$822.94	$822.95	$822.90