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	$46.43	9.858%	$51.0071	$51.01	$51.00	$51.00
Purchase #2	$31.59	5.325%	$33.2722	$33.27	$33.25	$33.30
Purchase #3	$241.82	5.816%	$255.8843	$255.88	$255.90	$255.90
Purchase #4	$215.43	12.739%	$242.8736	$242.87	$242.85	$242.90
Purchase #5	$63.39	11.184%	$70.4795	$70.48	$70.50	$70.50
Purchase #6	$216.39	4.411%	$225.935	$225.94	$225.95	$225.90
Purchase #7	$16.85	11.125%	$18.7246	$18.72	$18.70	$18.70
7 purchase totals =	$831.90		$898.1763	$898.17	$898.15	$898.20