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	$27.27	13.870%	$31.0523	$31.05	$31.05	$31.10
Purchase #2	$194.41	12.500%	$218.7113	$218.71	$218.70	$218.70
Purchase #3	$222.52	8.801%	$242.104	$242.10	$242.10	$242.10
Purchase #4	$63.50	4.732%	$66.5048	$66.50	$66.50	$66.50
Purchase #5	$233.70	10.173%	$257.4743	$257.47	$257.45	$257.50
Purchase #6	$146.38	9.585%	$160.4105	$160.41	$160.40	$160.40
Purchase #7	$165.86	13.277%	$187.8812	$187.88	$187.90	$187.90
7 purchase totals =	$1,053.64		$1,164.1384	$1,164.12	$1,164.10	$1,164.20