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	$57.61	3.792%	$59.7946	$59.79	$59.80	$59.80
Purchase #2	$124.51	4.575%	$130.2063	$130.21	$130.20	$130.20
Purchase #3	$107.70	5.341%	$113.4523	$113.45	$113.45	$113.50
Purchase #4	$37.77	9.669%	$41.422	$41.42	$41.40	$41.40
Purchase #5	$131.51	8.703%	$142.9553	$142.96	$142.95	$143.00
Purchase #6	$96.43	10.718%	$106.7654	$106.77	$106.75	$106.80
Purchase #7	$200.43	12.521%	$225.5258	$225.53	$225.55	$225.50
7 purchase totals =	$755.96		$820.1217	$820.13	$820.10	$820.20