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	$21.49	4.659%	$22.4912	$22.49	$22.50	$22.50
Purchase #2	$138.55	12.866%	$156.3758	$156.38	$156.40	$156.40
Purchase #3	$122.61	7.295%	$131.5544	$131.55	$131.55	$131.60
Purchase #4	$72.47	13.519%	$82.2672	$82.27	$82.25	$82.30
Purchase #5	$62.78	5.134%	$66.0031	$66.00	$66.00	$66.00
Purchase #6	$169.53	9.425%	$185.5082	$185.51	$185.50	$185.50
Purchase #7	$100.91	12.110%	$113.1302	$113.13	$113.15	$113.10
7 purchase totals =	$688.34		$757.3301	$757.33	$757.35	$757.40