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	$159.68	4.138%	$166.2876	$166.29	$166.30	$166.30
Purchase #2	$237.83	7.842%	$256.4806	$256.48	$256.50	$256.50
Purchase #3	$198.64	6.480%	$211.5119	$211.51	$211.50	$211.50
Purchase #4	$231.96	6.857%	$247.8655	$247.87	$247.85	$247.90
Purchase #5	$53.59	11.687%	$59.8531	$59.85	$59.85	$59.90
Purchase #6	$58.99	5.226%	$62.0728	$62.07	$62.05	$62.10
Purchase #7	$17.79	3.799%	$18.4658	$18.47	$18.45	$18.50
7 purchase totals =	$958.48		$1,022.5373	$1,022.54	$1,022.50	$1,022.70