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	$82.77	8.744%	$90.0074	$90.01	$90.00	$90.00
Purchase #2	$93.45	7.597%	$100.5494	$100.55	$100.55	$100.50
Purchase #3	$193.92	10.541%	$214.3611	$214.36	$214.35	$214.40
Purchase #4	$36.28	10.497%	$40.0883	$40.09	$40.10	$40.10
Purchase #5	$207.59	11.722%	$231.9237	$231.92	$231.90	$231.90
Purchase #6	$37.64	4.680%	$39.4016	$39.40	$39.40	$39.40
Purchase #7	$122.26	12.486%	$137.5254	$137.53	$137.55	$137.50
7 purchase totals =	$773.91		$853.8569	$853.86	$853.85	$853.80