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	$63.47	7.840%	$68.446	$68.45	$68.45	$68.40
Purchase #2	$240.85	11.839%	$269.3642	$269.36	$269.35	$269.40
Purchase #3	$113.51	12.307%	$127.4797	$127.48	$127.50	$127.50
Purchase #4	$96.62	9.327%	$105.6317	$105.63	$105.65	$105.60
Purchase #5	$173.45	3.140%	$178.8963	$178.90	$178.90	$178.90
Purchase #6	$52.93	3.430%	$54.7455	$54.75	$54.75	$54.70
Purchase #7	$75.64	12.455%	$85.061	$85.06	$85.05	$85.10
7 purchase totals =	$816.47		$889.6244	$889.63	$889.65	$889.60